Degradation of organic pollutants from water by biochar-assisted advanced oxidation processes: Mechanisms and applications

Effect of microplastics on tertiary/quaternary treatment of urban wastewater: Fe-biochar/peroxymonosulfate/sunlight vs solar photo-Fenton

Microplastics (MPs) are detected at various stages of urban wastewater treatment plants (UWTPs), however their impact on tertiary/quaternary treatments has been underexplored so far. This study evaluates the effect of MPs on the degradation of four micropollutants (carbamazepine, diclofenac, sulfamethoxazole, and trimethoprim) and the inactivation of total and antibiotic resistant (AR) E. coli in secondary treated urban wastewater (SUWW) through two advanced oxidation processes: iron-modified biochar with peroxymonosulfate (Fe-BC/PMS) under sunlight and solar photo-Fenton (SPF) with iron-EDDS at circumneutral pH. Aqueous matrix effect was also investigated comparing the effect in tap water with SUWW. The presence of high concentration of MPs (1.0 g/L) in tap water sped up micropollutants degradation (80 % removal in 20 min) for Fe-BC/PMS/sunlight treatment in comparison to MP absence condition (80 % removal only after 60 min). On the contrary, micropollutants degradation efficiency by SPF treatment in tap water decreased by 27 % in presence of MPs (1.0 g/L). MPs did not significantly affect micropollutants removal in SUWW. Moreover, MPs presence reduced E. coli inactivation (both total and AR E. coli) efficiency (2.2 log units) by Fe-BC/PMS/sunlight treatment, which was attributed to the UV light scattering/blocking effect. Pilot scale results in a raceway pond photoreactor for simultaneous micropollutants removal and bacteria inactivation in SUWW showed 60 % higher micropollutants degradation for SPF with EDDS (103 kJ/m2). Whereas Fe-BC/PMS/sunlight treatment achieved complete inactivation of E. coli (<2 CFU/100 mL) in comparison to SPF with Fe:EDDS (0.5 log unit reduction) after 45 min treatment (103 kJ/m2).

A comprehensive review of modified biochar-based advanced oxidation processes for environmental pollution remediation: efficiency, mechanism, toxicity assessment

Biochar (BC) has been demonstrated efficacy in activating oxidants to enhance environmental contaminant degradation. However, performance limitations of pristine biochar, including insufficient active sites and low electron transfer efficiency, primarily stemming from feedstock heterogeneity and pyrolytic parameter variations, resulting in suboptimal activation efficiency in practical applications. Recent studies demonstrated that targeted functionalization strategies, such as heteroatom doping, metal loading, and acid/alkali modification, could significantly improving activation performance of biochar, which was critical for advancing biochar-based advanced oxidation processes. In this review, the modification methods of biochar and their applications in activating diverse oxidants for water purification, soil remediation, air pollutant mitigation, and antimicrobial disinfection were summarized. Additionally, the differences in mechanisms among modified biochars for activating different oxidants in pollutant degradation were systematically illustrated. This review indicated that both free radicals and non-free radicals pathway played key roles in pollutant removal, either individually or through synergistic effects. Furthermore, potential challenges in applying modified biochar-based AOPs at a practical scale were also discussed. This review have shown that the presence of natural substances and impurities in these environments can deplete active components, resulting in reduced pollutant degradation efficiencies compared to controlled laboratory conditions. The current review illustrated that the toxicity of modified biochar was related to feedstocks and pyrolysis processes. Meanwhile, the toxicity of degradation intermediates could significantly reduce using modified biochar-based AOPs. Overall, this review provide insights for future research in this field.

Red mud-based magnetic biochar composite as a peroxydisulfate activator for tetracycline degradation

Red mud is the world's most extensively generated waste in the non-ferrous metal industry. Its utilization remains challenging, with disposal primarily relying on storage. Due to its strong alkalinity, it poses significant environmental risks. This study investigated the potential for high-value utilization of red mud-based catalyst, WR800, which was obtained via a one-step calcination method of red mud and wheat straw at high-temperature. The material effectively activated peroxydisulfate and achieved 97.7 % degradation of TC (20 mg/L) within 60 min. Singlet oxygen (1O2) and hydroxyl radicals (•OH) were identified as the active species. WR800 exhibited well pH adaptability and resilience to common anions, addressing challenges in real-world wastewater treatment. Additionally, the magnetic properties of WR800 facilitated its easy recovery, and it retained the ability to degrade 99.9 % of tetracycline even after four regeneration cycles. Turning red mud and wheat straw into a sustainable catalyst provides a low-cost and environmentally friendly solution for treating water polluted with antibiotics and is in line with circular economy principles. This study shows possible potential for industrial use in reducing antibiotic contamination and provides an idea for industrial and agricultural waste disposal.

Analysis of scientific and technological trends in the incorporation of activated carbon in advanced oxidation processes-a bibliometric study

There is high interest in the development of water pollution remediation technologies. Advanced oxidation processes (AOPs) are a promising alternative for the degradation of organic compounds; however, these technologies have been limited mainly by high operating costs and, in some cases, by forming byproducts, which can be more hazardous than the original pollutants. Activated carbon (AC) is a porous material that can be combined with AOP systems in various ways, given its adsorbent and catalytic characteristics. In addition, AC is a flexible, adaptable, and low-cost material. This article presents a bibliometric analysis of AOPs incorporating CA in scientific research and patents; the Scopus database was used to obtain patents and Orbit Express for patents. The most investigated AOPs incorporating AC are photocatalysis processes, Fenton processes, persulfate-based AOP, electrochemical processes, and ozonation. However, it is the persulfate-based AOP that has seen the greatest growth in scientific publications in recent years; this great interest can be related to the synergy that the process has with AC, allowing the degradation of contaminants via radical and non-radical. According to the maturity analysis of scientific publications, photocatalysis, Fenton, electrochemistry, ozonation, and persulfate technologies are in a growth stage and will reach maturity in 2034, 2042, 2040, 2034, and 2035, respectively; these technologies coupled with AC are expected to generate a greater number of patents when they reach maturity.

Densely distributed Co onto carbon-layer-coated flower-like Ni/Al2O3 and its tailored integration into a stirrer for multiple catalytic degradation and solar-powered water evaporation

Multiple functional tailored materials have shown great potential for both pollutant degradation and freshwater recovery. In this study, we synthesized densely distributed Co onto carbon-layer-coated Ni/Al2O3 hydrangea composites (Ni/Al2O3@Co) via the polymerization of dopamine under a controlled graphitized process. The characterization results revealed that Ni/Al2O3@Co, with abundant exposed bimetallic Co-Ni species on the surface of Al2O3, could afford accessible catalytic sites for persulphate activation and subsequent pollutant degradation. The tetracycline (TC) degradation rate of optimal Ni/Al2O3@Co500 reached 98.1% within 15 min with a first-order rate constant of 0.498 min-1, which is ∼1.38 times that of Al2O3@Co500 (0.362 min-1), indicating the existing Co-Ni intermetallic synergy. Free radical quenching experiments indicated that ˙O2- plays a leading role in the catalytic degradation of TC. Moreover, Ni/Al2O3@Co500 afforded strong flexibility for the degradation of methylene blue (MB), norfloxacin (NFX), bisphenol A (BPA), and oxytetramycin (OTC). Ni/Al2O3@Co500 catalysts were anchored onto a customized sponge via a calcium-triggered hydrogel crosslink strategy to construct an integral and tailored stirrer, which was used directly as the mechanical stirrer catalyst for the activation of peroxymonosulfate and pollutant removal. This obtained stirrer was also used as a monolith evaporator affording an evaporation rate of 1.944 kg m-2 h-1 at a solar-driven photothermal interface. We also demonstrated that the shape of the tailored sponge weakly affects the course of the degradation reaction. Furthermore, the degradation rates of TC in actual water sources on a Ni/Al2O3@Co500 sponge were still maintained up to 90% with rational recycling properties, which provide a promising solution for the multiple-functional pollutant degradation and water regeneration.

Effect of persulfate dosage on organic degradation using N-doped biochar: Reaction pathway and environmental implications

Persulfate-based advanced oxidation processes (PS-AOPs) catalyzed by carbon-based catalysts are promising for removing organic pollutants via radical/non-radical pathways. However, the activation efficiency of peroxymonosulfate (PMS) or peroxydisulfate (PDS) usage and the reaction mechanism remain insufficiently understood. In this study, the effects of PMS/PDS dosage on the degradation of bisphenol A (BPA, 10 mg/L) were evaluated using N-doped biochar (N-BC, 0.2 g/L) assisted PS-AOPs. The reaction pathways were comprehensively investigated through a combination of characterization techniques and molecular simulations. With low PS dosages (0.05 and 0.1 mM), the degradation rate constants (k obs $$ {k}_{obs} $$ ) were higher in N-BC/PDS (0.04 and 0.07 min-1) compared to N-BC/PMS (0.02 and 0.04 min-1), likely due to higher PDS utilization, which enhanced the contribution of the non-radical pathway. Interestingly, with higher PS dosages (0.5 and 1.5 mM), thek obs $$ {k}_{obs} $$ values were 0.16 min-1 and 0.18 min-1 in N-BC/PMS, respectively, significantly exceeding those determined in N-BC/PDS (0.11 and 0.11 min-1). This result stemmed from the greater adsorption capacity of N-BC for PMS compared to PDS, leading to increased formation of 1O2. The contribution of non-radical pathways for both PMS and PDS increased with higher PS dosage. The results highlighted that BPA degradation improved significantly with the increase in PMS dosage; meanwhile, BPA degradation was insensitive to PDS dosage. The optimal PMS dosage for BPA degradation was found to be 1.5 mM and 0.1 mM for PDS. This study offered valuable insights for optimizing PS-AOPs in environmental remediation, helping to guide the selection of appropriate oxidants and dosages for maximizing pollutant removal. PRACTITIONER POINTS: Effect of PMS/PDS dosage on BPA degradation by N-doped biochar was revealed. Contribution of dominated non-radical pathway increased as PMS/PDS dosage increased. The greater PDS utilization and non-radical pathway resulted in the higherk obs $$ {k}_{obs} $$ at low dosage. N-BC adsorbed more PMS than PDS, leading to an increase ink obs $$ {k}_{obs} $$ at high dosage.

Enhanced degradation of sulfamethoxazole in water by biochar loading and multiple free and non-free radicals cooperating in the Fe7S8@BC/PS system

The excessive consumption of sulfamethoxazole (SMX), a pharmaceutical antibiotic, poses significant environmental hazards. The Fe7S8-persulfate (Fe7S8-PS) system has been employed for SMX remediation because of its excellent performance. However, Fe7S8 tends to agglomerate and become passivated, negatively impacting its activation performance. In this study, the incorporation of Fe7S8 into biochar (BC) effectively reduced agglomeration and enhanced the catalytic performance. The PS activated by Fe7S8@BC loaded at a mass ratio of 1:1 exhibited the highest SMX removal efficiency (92.5%). The free radicals (·OH, SO4·-, and O2·-) and non-free radicals (1O2 and Fe(IV)) were identified during PS activation. The removal of SMX was found to be dependent on the contribution of ·OH, SO4·-, 1O2 and Fe(IV), rather than O2·-. Additionally, the presence of C-O-Fe in Fe7S8@BC, which formed the framework of the primary battery, contributed to the enhanced degradation of SMX. The toxicity prediction results demonstrated a significant reduction in the toxicity of the transformation byproducts. Hence, the mechanism of PS activation was explored through Fe7S8@BC, proposing novel strategies for developing advanced and efficient approaches to SMX removal.

Construction of Anthracene-based Metal-Organic Framework Exhibiting Enhanced Singlet Oxygen Storage and Release Capabilities for Efficient Photodegradation of Phenolic Pollutants

Controlling the generation and release of singlet oxygen (1O2) with high oxidation activity and long lifetime properties holds significant potential for efficient oxidation of permanent organic pollutants, tumor eradication, and targeted molecular oxidation. However, the conditions for controlled generation and release of 1O2 remain unclear. Hence, the novel anthracene-ligands based Zr-MOFs which use acetic acid (HAc) are constructed to optimize the surface defects and specific surface area exhibit ultrafast saturation adsorption capacity (362.60 mg g-1 in 60 s) and deep photodegradation performance toward bisphenol A (BPA) in water (50 ppm in 20 min) via Zr-DPA MOF-1HAc. Mechanistic studies have shown that MOFs are capable of generating high concentrations of 1O2, while anthracene ligands can rapidly store 1O2 and form endoperoxides (EPOs), which can be rapidly released under external light, heat, or chemical triggering conditions. Thus, high concentration of 1O2 is always involved in the oxidation reaction throughout the whole photodegradation process and ultimately achieves the complete mineralization of target phenolic pollutant molecules. This innovative strategy has important implications for generating, storing and controlling the release of 1O2 in the field of environmental engineering and chemical synthesis.

Upcycling Waste Biomass to Biochar: Feedstocks, Catalytic Mechanisms, and Applications in Advanced Oxidation for Wastewater Decontamination

Advanced oxidation technology plays an important role in wastewater treatment due to active substances with high redox potential. Biochar is a versatile and functional biomass material. It can be used for resource management of various waste biomasses. In addition, carbonaceous materials are commonly used to enhance the synergistic mechanisms of advanced oxidation processes, because of their good electrical conductivity and metal-free leaching. Biochar produced from waste biomass through pyrolysis has catalytic potential, is cost-effective, and is environmentally friendly. It is commonly used to activate hydrogen peroxide, persulfate, ozone, photocatalysis, and other systems for degrading organic pollutants in water. This review provides a summary of the feedstocks, pyrolysis conditions, and modification methods used in biochar production. It also described the effects of these factors on the yield, structure, and active sites of the biochar. The review summarized the mechanisms of various catalytic systems and their applications in wastewater decontamination, as well as their potential for practical application. Eventually, the limitations of this current technique and the outlook for future research were noted.

Intrinsic structure-function connections of carbon-encapsulated nanoscale zero-valent-iron using various pyrolysis atmospheres

Carbon-encapsulated nanoscale zero-valent-iron (C@Fe0) derived from plant-based extracts has been the subject of growing interest due to its environmental friendliness. However, the effects of various pyrolysis atmospheres on the structure-function connections of C@Fe0 are still unclear. In this study, three pyrolytic atmospheres, namely Air, N2, and 5% H2/Ar were selected to fabricate X-C@Fe0 (X represented as A, N, H) for removing 2,4,6-Trichlorophenol (TCP), and the relationships between their structures and functions were demonstrated. The N-C@Fe0 with improved hydrophobicity exhibited superior TCP adsorptive performance compared to H-C@Fe0 and A-C@Fe0. Apart from this, N-C@Fe0 effectively reduced TCP through dechlorination, this process achieved 25.9% dichlorination efficiency, and in turn alleviated products toxicity. Electrochemical tests and density functional theory calculations showed that the substitution of nitrogen with carbon in N-C@Fe0 elevated the Fe-d band center and enhanced the hybridization between Fe-3d and C-2p orbital, which collectively promoted the dichlorination of TCP. This study will provide practical guideline for improving the intrinsic activity of iron-carbon materials using pyrolytic atmosphere engineering.

A tartaric acid (TA)-coated iron-based biochar as heterogeneous fenton catalyst for enhanced degradation of dibutyl phthalate

Iron-biochar composite is a promising catalyst in Fenton-like system for removal of organic pollutants. Nevertheless, low cycling rate of Fe(III)/Fe(II), high iron leaching and low H2O2 utilization efficiency impedes its application. Herein, a iron-based biochar (C-Fe) coated with tartaric acid (TA) was synthesized. The specific structure of inherent graphitized carbon and TA coating improved the removal efficiency of dibutyl phthalate (DBP) to 93%, promoted 2-fold increase in HO• production in H2O2 activation, improved the cycling rate of Fe(III)/Fe(II), and mitigated Fe leaching significantly. The developed HO• and 1O2 dominated Fenton-like system had an excellent pH universality and anti-interference to inorganic ions and real water matrixes. Moreover, C-Fe-TA has been shown to efficiently degrade DBP by using the dissolved oxygen in water to generate HO•. This work provided a novel insight for sustainable and efficient HO• and 1O2 generation, which motivated the development of new water treatment technology based on efficient iron-biochar catalyst.

Efficient activation of peroxymonosulfate by N-doped waste herb senna obtusifolia biochar for degrading NPX: Synergistic effect of carbonyl and nitrogen sites

In this work, waste herb senna obtusifolia was utilized as the biochar precursor, and a N-doped biochar (NSOBC-6) was prepared to activate peroxymonosulfate (PMS) for degrading Naproxen (NPX). NSOBC-6 exhibited superior catalytic performance in activating PMS, which could degrade NPX completely within 60 min. The NSOBC-6/PMS system also had good reusability and effectiveness under a wide range of pH values and high salinity conditions. The significant contribution of singlet oxygen (1O2) and superoxide radicals (O2•-) in NPX degradation was revealed. The results of XPS and DFT calculations indicated C=O, pyridinic-N and graphitic-N participated as catalytic sites in the degradation of NPX. The differences in electron density and the ELUMO-EHOMO (ΔELUMO-HOMO) gap were induced by N doping, enhancing the PMS activation capacity of NSOBC-6. This work presented a strategy to convert waste herbal into functional biochar materials, which was of great significance for the development of green and efficient catalysts.

Application of Biochar-Based Materials for Effective Pollutant Removal in Wastewater Treatment

With the growth of the global population and the acceleration of industrialization, the problem of water pollution has become increasingly serious, posing a major threat to the ecosystem and human health. Traditional water treatment technologies make it difficult to cope with complex pollution, so the scientific community is actively exploring new and efficient treatment methods. Biochar (BC), as a low-cost, green carbon-based material, exhibits good adsorption and catalytic properties in water treatment due to its porous structure and abundant active functional groups. However, BC's pure adsorption or catalytic capacity is limited, and researchers have dramatically enhanced its performance through modification means, such as loading metals or heteroatoms. In this paper, we systematically review the recent applications of BC and its modified materials for water treatment in adsorption, Fenton-like, electrocatalytic, photocatalytic, and sonocatalytic systems, and discuss their adsorption/catalytic mechanisms. However, most of the research in this field is at the laboratory simulation stage and still needs much improvement before it can be applied in large-scale wastewater treatment. This review improves the understanding of the pollutant adsorption/catalytic properties and mechanisms of BC-based materials, analyzes the limitations of the current studies, and investigates future directions.

Sustainability-inspired upcycling of plastic waste into porous carbon nanobulks for water decontamination via peroxymonosulfate activation

"White pollution" is regarded as one of the most serious problems in the natural environment. Thus greener recycling of plastic waste has attracted significant efforts in recent research. In this study, to kill two birds with one stone, a series of porous carbon nanobulks (PCNs) were synthesized from the pyrolysis of plastic waste (polyethylene terephthalate, PET) and inorganic salt (including NaHCO3, Na2CO3, NaCl, and ZnCl2) for sulfadiazine (SDZ) degradation via peroxymonosulfate (PMS) activation. PCNs-1 (co-calcinated from PET and NaHCO3) with a large number of CO and COOH active sites, which were in favor of PMS activation and electron transfer during the catalytic process, had shown the best catalytic activity for SDZ degradation. Significantly, PCNs-1 exhibited excellent universality, adaptability, and stability. The degradation pathways of SDZ were identified by the total content of organic carbon (TOC), and high-resolution mass spectrometry (HR-MS). The possible mechanism was proposed according to the anion effect, quenching experiments, electron paramagnetic resonance (EPR), and electrochemical analysis, indicating that radical (OH, SO4-, O2-) and non-radical (1O2 and e) species were the catalytically active species for SDZ decomposition in the PCNs-1/PMS system. Moreover, Ecological Structure-Activity-Relationship Model (ECOSAR) program and wheat seed cultivation experiments clearly demonstrated that the biotoxicity of SDZ could be effectively reduced by the PCNs-1/PMS system. Here we successfully upcycled plastic waste into high-value materials for efficient water decontamination.

Efficient oxidative remediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soil: A thorough comprehension of Fe-loaded biochar activated persulfate

The porous and defective structure of biochar (BC) can accelerate surface electron transfer, promote the generation of more reactive oxygen species (ROS) by persulfate (PS), and effectively degrade organic pollutants in the soil. Electron transfer is a crucial link in this process, directly determining its oxidative degradation efficiency. In this study, using a novel strategy of enhancing electron transfer on the surface of BC by loading iron, three Fe-loaded BC activators (Fe-FeOx@BC, Fe2O3@BC and Fe3O4@BC) were synthesized to support the oxidative remediation of benzo(a)pyrene (BaP, Model compound of PAHs)-contaminated soil by PS. The results showed that Fe3O4@BC supported PS oxidation and remediation of BaP-contaminated soil had the best effect among the three BC-based activators, and the reuse effect was stable. Under the conditions of Fe3O4@BC addition of 1.00 wt%, PS addition of 0.75 wt%, reaction temperature of 35 °C, and solid-liquid ratio of 1:2.5, the removal rate of BaP in the soil reached the maximum of 93.84% at 120 min, and the soil toxicity was significantly reduced after remediation. The defect structure, conductive magnetic particles, and active functional groups on the surface of Fe3O4@BC were the key factors for activating PS to degrade BaP. With the combined action of the free radical pathway caused by ROS and the non-free radical pathway caused by 1O2, electron transfer, and active functional groups, BaP was degraded to small molecules such as CO2 and H2O, achieving rapid and efficient remediation of organic contaminated soil.

Urban wastewater disinfection by FeCl3-activated biochar/peroxymonosulfate system: Escherichia coli inactivation and microplastics interference

Biochar coupled with peroxymonosulfate (PMS) to produce sulfate radicals and its application to urban wastewater disinfection has been rarely investigated and no information is available about microplastics (MPs) interference on the disinfection process. In this study, FeCl3-activated biochar (Fe-BC) was coupled to PMS to evaluate the inactivation of Escherichia coli (E. coli) in real secondary treated urban wastewater. Surface morphology of Fe-BC sample, characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), showed a rough texture with uniform distribution of iron particles over the entire surface area. E. coli inactivation improved (∼3.8 log units, detection limit = 1 CFU/100 mL) as Fe-BC concentration was decreased (from 1.0 g/L to 0.5 g/L), at a constant PMS dose (300 mg/L). Besides, removal efficiency of E. coli was negatively affected by the presence of small (30-50 μm) polyethylene MPs (PE MPs) (200 mg/L), which could be attributed to the adsorption of MPs on Fe-BC surface, according to SEM images of post-treated Fe-BC. The low disinfection efficiency of Fe-BC/PMS system in presence MPs could be due to blocking of Fe-BC sites for PMS activation and/or radicals scavenging during treatment. These results allowed to unveil the mechanisms of MPs interference on E. coli inactivation by Fe-BC/PMS, as well as the potential of this process to make the effluent in compliance with the stringent limit for agricultural reuse.

Enhanced simazine degradation via peroxymonosulfate activation using hemin-doped rice husk biochar as a novel Fe/N-C catalyst

The presence of herbicides, including simazine (SIM), in aquatic environments pose significant threats to these ecosystems, necessitating a method for their removal. In this study, a hemin-doped rice husk-derived biochar (RBC@Hemin20%) was synthesized using a simple, one-step pyrolysis, and its degradation efficiency towards SIM via peroxymonosulfate (PMS) was assessed. Under optimized conditions (hemin loading = 20 wt%, SIM = 0.5 ppm, RBC@Hemin20% catalyst = 0.2 g L-1, PMS = 2.0 mM, and pH = 5.84 [unadjusted]), RBC@Hemin20%, as an Fe/N-C catalyst, could activate PMS to achieve >99% degradation of SIM. Based on radical scavenger and electron spin resonance spectroscopy (ESR) experiments, both radical (•OH and SO4•-) and non-radical (such as singlet oxygen, 1O2) mechanisms and electron transfer were involved in the degradation system. Significant mineralization (97.3%) and reusability efficiency (∼74.1% SIM degradation after 4 applications) were exhibited by the RBC@Hemin20%/PMS system, which also maintained a remarkable degradation efficiency in tap-, river-, and ground-water. Additionally, the RBC@Hemin20%/PMS system exhibited rapid degradation of tetracycline (TC) and diclofenac (DCF), indicating its prospects in the degradation of other organic pollutants of aquatic environments. The plausible degradation mechanism pathways of SIM are proposed based on identified intermediates. Finally, the toxicity of these intermediate products is analysed using the Ecological Structure Activity Relationship (ECOSAR) software. It is expected that this study will expand the current knowledge on the synthesis of efficient biomass-based Fe/N-C composites for the removal of organic pollutants in water.

Synergistic degradation of 2,4-dichlorophenoxyacetic acid in water by interfacial pre-reduction enhanced peroxymonosulfate activation derived from novel zero-valent iron/biochar

Iron-based biochar exhibits great potential in degrading emerging pollutants and remediation of water environments. In this study, a highly efficient catalytic Fe0/biochar (MZB-800) was synthesized by the co-pyrolysis of poplar sawdust and K2FeO4 at 800 °C. A novel water purification technology of pre-reduction followed by PMS activation for MZB-800 was proposed to degrade the refractory 2,4-dichlorophenoxyacetic acid (2,4-D) pesticide. The corrosive effect of the strong oxidizing potassium salt endowed the MZB-800 surface with more Fe0 and porous structure, achieving greater 2,4-D adsorption binding energy. The removal efficiency of MZB-800 on 2,4-D was greater than that of biochar (BC) and conventional Fe0/biochar (Fe-BC) prepared by FeCl3·6 H2O as the precursor. The proposed novel water purification technology showed the synergistic effect between the interfacial pre-reduction and the PMS activation derived by MZB-800. Regarding 2,4-D degradation and dechlorination performance, the synergistic coefficient between pre-reduction and subsequent PMS activation for MZB-800 were 2 and 1.4 respectively. Based on the normalized kinetic analysis and the Langmuir-Hinshelwood model, we proposed the underlying mechanism of MZB-800 interfacial pre-reduction and subsequent PMS activation for synergistic removal of 2,4-D. The large amount of Fe2+ and hydroxyl density accumulated by the Fe0 and hydroquinone structures on the MZB-800 surface during the pre-reduction stage provided abundant active sites for the subsequent activation of PMS. The improved activation reaction rate generated more reactive oxygen species, further strengthening the removal efficiency of 2,4-D. This work manifested that the novel water purification technology of pre-reduction/PMS activation of iron-based biochar is feasible for removing emerging pollutants in the water environment. ENVIRONMENTAL IMPLICATION: Extensive abuse of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide with high solubility and refractory degradation has caused environmental pollution and ecological deterioration. This manuscript described a novel water purification technology, centered on high-efficiency Fe0/biochar and utilizing pre-reduction and PMS reactivation strategies to synergistically degrade 2,4-D, which had strong environmental relevance. By elucidating the synergistic removal mechanism, the research provided valuable insights into removing emerging pollutants, thus promoting environmental sustainability and safeguarding ecosystem health. Overall, it is of high importance to provide a feasible and efficient method for removing hazardous 2,4-D from water environments, which contributes to addressing pressing environmental problems.

Biochar-based composites for removing chlorinated organic pollutants: Applications, mechanisms, and perspectives

Chlorinated organic pollutants constitute a significant category of persistent organic pollutants due to their widespread presence in the environment, which is primarily attributed to the expansion of agricultural and industrial activities. These pollutants are characterized by their persistence, potent toxicity, and capability for long-range dispersion, emphasizing the importance of their eradication to mitigate environmental pollution. While conventional methods for removing chlorinated organic pollutants encompass advanced oxidation, catalytic oxidation, and bioremediation, the utilization of biochar has emerged as a prominent green and efficacious method in recent years. Here we review biochar's role in remediating typical chlorinated organics, including polychlorinated biphenyls (PCBs), triclosan (TCS), trichloroethene (TCE), tetrachloroethylene (PCE), organochlorine pesticides (OCPs), and chlorobenzenes (CBs). We focus on the impact of biochar material properties on the adsorption mechanisms of chlorinated organics. This review highlights the use of biochar as a sustainable and eco-friendly method for removing chlorinated organic pollutants, especially when combined with biological or chemical strategies. Biochar facilitates electron transfer efficiency between microorganisms, promoting the growth of dechlorinating bacteria and mitigating the toxicity of chlorinated organics through adsorption. Furthermore, biochar can activate processes such as advanced oxidation or nano zero-valent iron, generating free radicals to decompose chlorinated organic compounds. We observe a broader application of biochar and bioprocesses for treating chlorinated organic pollutants in soil, reducing environmental impacts. Conversely, for water-based pollutants, integrating biochar with chemical methods proved more effective, leading to superior purification results. This review contributes to the theoretical and practical application of biochar for removing environmental chlorinated organic pollutants.

Interaction and band structure-determined inhibition of negative Cr (VI) and positive Fe (III) for antibiotic photodegradation by nitrogen-doped dissolved black carbon

The influences of the positive Fe3+ and the negative Cr2O72- on the tetracycline (TC) photodegradation by N-doped dissolved black carbon (NDBC) have been investigated in this work. A series of samples (NDBC300, NDBC400 and NDBC500) have been extracted from the corresponding biochar. NDBC400 has the best photodegradation performance (79%) for TC under visible light irradiation. Adding Cr2O72- and Fe3+ can reduces TC photodegradation efficiency into 37% and 53%, respectively. This maybe from that Cr2O72- has stronger interaction with NDBC400 than Fe3+ since it can quench more fluorescence intensity of NDBC400 than Fe3+. Furthermore, Cr2O72- can reduce the steady-state concentration of 3NDBC400*, 1O2 and •OH, whereas Fe3+can just reduce the steady-state concentration of 3NDBC400* and increase the concentration of •OH. This may explain why Cr2O72- has stronger inhibit performance of TC photodegradation by NDBC400 than Fe3+. The band structures of NDBC400, NDBC400-Fe3+ and NDBC400-Cr2O72- are constructed. And the VB of NDBC400-Fe3+ has a stronger ability to produce •OH than NDBC400. In summary, coupling interaction and band structure characterization of NDBC400, NDBC400-Fe3+ and NDBC400-Cr2O72- can explain well why Cr2O72 has stronger inhibition effect than Fe3+ and Fe3+ can increase the concentration of •OH. This work provides a deep insight for the photochemical behavior of dissolved black carbon and the transformation behavior of the co-existed metal ions and antibiotics.

Valorization of Field-Spent Granular Activated Carbon as Heterogeneous Ozonation Catalyst for Water Treatment

Developing sustainable cost-effective strategies for valorization of field-spent granular activated carbon (s-GAC) from industrial water treatment has gained much interest. Here, we report a cost-effective strategy for the regeneration of s-GAC as an adsorbent in a large-scale drinking water treatment plant and used as an efficient and durable ozonation catalyst in water. To achieve this, a series of samples is prepared by subjecting s-GAC to thermally controlled combustion treatments with and without pyrolysis. The catalytic performance of the optimized sample is evaluated for oxalic acid degradation as the model pollutant under batch (>15 h) and continuous flow operations (>200 h). The partially deactivated catalyst upon reuse is restored by thermal treatment. Electron paramagnetic resonance and selective quenching experiments show the formation of singlet oxygen (1O2) during catalytic ozonation. The GAC-ozonation catalyst is efficient to minimize the formation of chlorinated disinfection by-products like trihalomethanes and haloacetic acids in an urban wastewater effluent.

A review on titanium oxide nanoparticles modified metal-organic frameworks for effective CO2 conversion and efficient wastewater remediation

Environmental pollution has been increasing since last decade due to increasing industrialisation and urbanisation. Various kinds ofenvironmental pollutants including carbon dioxide (CO2), dyes, pharmaceuticals, phenols, heavy metals along with many organic and inorganic species have been discovered in the various environmental compartments which possess harmful impacts tox human health, wildlife, and ecosystems. Thus, various efforts have been made through regulations, technological advancements, and public awareness campaigns to reduce the impact of the pollution. However, finding suitable alternatives to mitigate their impacts remained a challenge. Metal-organic frameworks (MOFs) are one of the advanced materials with unique features such as high porosity and stability which exhibit versatile applications in environmental remediation. Their composites with titanium oxide nanoparticles (TiO2) have been discovered to offer potential feature such as light harvesting capacity and catalytic activity. The composite integration and properties have been confirmed through characterization using surface area analysis, scanning electron/transmission electron microscopy, atomic force microscopy, fourier transformed infrared spectroscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, and others. Thus, this work rigorously discussed potential applications of the MOF@TiO2 nanomaterials for the CO2 capture and effective utilization in methanol, ethanol, acetone, acetaldehyde, and other useful products that served as fuel to various industrial processes. Additionally, the work highlights the effective performance of the materials towards photocatalytic degradation of both organic and inorganic pollutants with indepth mechanistic insights. The article will offer significant contribution for the development of sustainable and efficient technologies for the environmental monitoring and pollution mitigation.

The boom era of emerging contaminants: A review of remediating agricultural soils by biochar

Emerging contaminants (ECs) are widely sourced persistent pollutants that pose a significant threat to the environment and human health. Their footprint spans global ecosystems, making their remediation highly challenging. In recent years, a significant amount of literature has focused on the use of biochar for remediation of heavy metals and organic pollutants in soil and water environments. However, the use of biochar for the remediation of ECs in agricultural soils has not received as much attention, and as a result, there are limited reviews available on this topic. Thus, this review aims to provide an overview of the primary types, sources, and hazards of ECs in farmland, as well as the structure, functions, and preparation types of biochar. Furthermore, this paper emphasizes the importance and prospects of three remediation strategies for ECs in cropland: (i) employing activated, modified, and composite biochar for remediation, which exhibit superior pollutant removal compared to pure biochar; (ii) exploring the potential synergistic efficiency between biochar and compost, enhancing their effectiveness in soil improvement and pollution remediation; (iii) utilizing biochar as a shelter and nutrient source for microorganisms in biochar-mediated microbial remediation, positively impacting soil properties and microbial community structure. Given the increasing global prevalence of ECs, the remediation strategies provided in this paper aim to serve as a valuable reference for future remediation of ECs-contaminated agricultural lands.

Visualization of phenanthrene effect on biochar colloids transport in porous media

Biochar colloids (BCs) can be used as adsorbent materials for remediation of phenanthrene due to their high specific surface area and other characteristics. Understanding the effects of phenanthrene on the transport of BCs contributes to facilitate the removal of phenanthrene in soil and water habitats. In this work, the influence of phenanthrene on the transport of BCs under different environmental factors (pH, ionic strength (IS), media size) in a one-dimensional sand column was firstly explored together with a real-time visualization system to explore the transport mechanism of BCs in two-dimensional sand tank. The results show that phenanthrene adsorbed on the surface of BCs, shielded its surface charge and reduced the mobility of BCs in porous media. Acidic conditions promoted the agglomeration of BCs and adsorption of phenanthrene, resulting in a 51.03 % decrease in the maximum breakthrough rate of BCs compared to alkaline conditions. The same was true for the high IS condition, where the maximum breakthrough rate of BCs was only 0.95 % at IS = 50. Additionally, there was a substantial and positive correlation between media particle size and BCs mobility. As the quartz sand particle size increased, the maximum breakthrough rates of BCs were 2.67 %, 33.28 %, and 52.27 % in the 1-D experiment, and 0, 13.88 %, and 13.10 % in the 2-D experiment, respectively. The contact area of BCs with the medium expands under the fine particle size condition, leading to a significant decrease in the mobility of BCs at low potentials influenced by phenanthrene. This finding is significant for biochar application in phenanthrene contaminated soil and groundwater remediation.

A state-of-art review on the redox activity of persistent free radicals in biochar

Biochar-bound persistent free radicals (biochar-PFRs) attract much attention because they can directly or indirectly mediate the transformation of contaminants in large-scale wastewater treatment processes. Despite this, a comprehensive top-down understanding of the redox activity of biochar-PFRs, particularly consumption and regeneration mechanisms, as well as challenges in redox activity assessment, is still lacking. To tackle this challenge, this review outlines the identification and determination methods of biochar-PFRs, which serve as a prerequisite for assessing the redox activity of biochar-PFRs. Recent developments concerning biochar-PFRs are discussed, with a main emphasis on the reaction mechanisms (both non-free radical and free radical pathways) and their effectiveness in removing contaminants. Importantly, the review delves into the mechanism of biochar-PFRs regeneration, triggered by metal cations, reactive oxygen species, and ultraviolet radiations. Furthermore, this review thoroughly explores the dilemma in appraising the redox activity of biochar-PFRs. Components with unpaired electrons (particular defects and metal ions) interfere with biochar-PFRs signals in electron paramagnetic resonance spectra. Scavengers and extractants of biochar-PFRs also inevitably modify the active ingredients of biochar. Based on these analyses, a practical strategy is proposed to precisely determine the redox activity of biochar-PFRs. Finally, the review concludes by presenting current gaps in knowledge and offering suggestions for future research. This comprehensive examination aims to provide new and significant insights into the redox activity of biochar-PFRs.

Facile synthesis of pyrite FeS2 on carbon spheres for high-efficiency Fenton-like reaction

Designing iron-based catalysts for Fenton-like reactions with peroxymonosulfate (PMS) as oxidants have attracted growing attentions. Herein, pyrite FeS2 supported on carbon spheres (FeS2@C) is synthesized by a facile low-temperature method. The FeS2@C/PMS system can degrade carbamazepine (CBZ) effectively in a wide pH range. Sulfate radicals (SO4·-), hydroxyl radicals (·OH), superoxide radical (O2·-), and singlet oxygen (1O2) are the responsible reactive oxygen species (ROSs) for CBZ degradation. Moreover, in the simulated fixed-bed reactor, the FeS2@C/PMS system can maintain a high CBZ removal ratio of >95% for than 8 h, exhibiting its excellent stability. The outstanding performance of FeS2@C/PMS system is attributed to the presence of carbon spheres and lattice S2-, which together promote the Fe(III)/Fe(II) redox cycle. The FeS2@C is a promising catalyst due to its facile synthesis, low cost, high efficiency, and excellent stability to activate PMS for organics degradation.

Rational synthesis of two isostructural thiophene-containing metal-organic frameworks toward photocatalytic degradation of organic pollutants

In this work, thiophene moieties (as the crucial functional groups) have been successfully incorporated into the skeleton of metal-organic frameworks (MOFs) by using thienyl-substituted triazole ligands. Reaction of AgCF3SO3 with 3-phenyl-5-(2-thienyl)-1,2,4-triazole (PTTzH) or 3,5-bis(2-thienyl)-1,2,4-triazole (BTTzH) afforded two isostructural MOFs (AgTz-3 and AgTz-4) in gram-scale. AgTz-4 with higher thiophene content showed significantly stronger photocatalytic activity than AgTz-3 with lower thiophene content. Noteworthy, the photodegradation rate constants of AgTz-4 were 0.055 mg·L-1·min-1 for rhodamine B and 0.24 min-1 for salazosulfapyridine, which is comparable or even higher than some MOF-based materials reported in the literature. More importantly, AgTz-4 demonstrated good reusability and stability after four cycles of photodegradation. Our experimental results revealed that the enhanced photodegradation efficiency can be attributed to the increased light absorption capacity and optimized band structure of Ag-MOFs resulting from the introduction of thiophene groups into MOF structures.

Influence mechanism of anions on iron doping into swine bone char: Promoting non-radical oxidation of acetaminophen in a Fenton-like system

The application of iron-doped biochar in peroxymonosulfate (PMS) activation systems has gained increasing attention due to their effectiveness and environmental friendliness in addressing environmental issues. However, the behavioral mechanism of iron doping and the detailed 1O2 generation mechanism in PMS activation systems remain ambiguous. Here, we investigated the effects of three anions (Cl-, NO3-and SO42-) on the process of iron doping into bone char, leading to the synthesis of three iron-doped bone char (Fe-ClBC, Fe-NBC and Fe -SBC). These iron-doped bone char were used to catalyze PMS to degrade acetaminophen (APAP) and exhibited the following activity order: Fe-ClBC > Fe-NBC > Fe-SBC. Characterization results indicated that iron doping primarily occurred through the substitution of calcium in hydroxyapatite within BC. In the course of the impregnation, the binding of SO42- and Ca2+ hindered the exchange of iron ions, resulting in lower catalytic activity of Fe-SBC. The primary reactive oxygen species in the Fe-ClBC/PMS and Fe-NBC/PMS systems were both 1O2. 1O2 is produced through O2•- conversion and PMS self-dissociation, which involves the generation of metastable iron intermediates and electron transfer within iron species. The presence of oxygen vacancies and more carbon defects in the Fe-ClBC catalyst facilitates 1O2 generation, thereby enhancing APAP degradation within the Fe-ClBC/PMS system. This study is dedicated to in-depth exploration of the mechanisms underlying iron doping and defect materials in promoting 1O2 generation.

Biochar-Derived Persistent Free Radicals: A Plethora of Environmental Applications in a Light and Shadows Scenario

Biochar (BC) is a carbonaceous material obtained by pyrolysis at 200-1000 °C in the limited presence of O2 from different vegetable and animal biomass feedstocks. BC has demonstrated great potential, mainly in environmental applications, due to its high sorption ability and persistent free radicals (PFRs) content. These characteristics enable BC to carry out the direct and PFRs-mediated removal/degradation of environmental organic and inorganic contaminants. The types of PFRs that are possibly present in BC depend mainly on the pyrolysis temperature and the kind of pristine biomass. Since they can also cause ecological and human damage, a systematic evaluation of the environmental behavior, risks, or management techniques of BC-derived PFRs is urgent. PFRs generally consist of a mixture of carbon- and oxygen-centered radicals and of oxygenated carbon-centered radicals, depending on the pyrolytic conditions. Here, to promote the more productive and beneficial use of BC and the related PFRs and to stimulate further studies to make them environmentally safer and less hazardous to humans, we have first reviewed the most common methods used to produce BC, its main environmental applications, and the primary mechanisms by which BC remove xenobiotics, as well as the reported mechanisms for PFR formation in BC. Secondly, we have discussed the environmental migration and transformation of PFRs; we have reported the main PFR-mediated application of BC to degrade inorganic and organic pollutants, the potential correlated environmental risks, and the possible strategies to limit them.

A Comprehensive Review on Modification of Titanium Dioxide-Based Catalysts in Advanced Oxidation Processes for Water Treatment

It has become necessary to develop effective strategies to prevent and reduce water pollution as a result of the increase in dangerous pollutants in water reservoirs. Consequently, there is a need to design new catalyst materials to promote the efficiency of advanced oxidation processes (AOPs) in the field of wastewater treatment plant to ensure the mineralization of trace organic contaminants. A notable approach gaining attention involves the coupling of sulfate radicals-based AOPs to photocatalysis or electrocatalysis processes, aiming to achieve the complete removal of refractory contaminants into water and carbon dioxide. Titanium dioxide as metal oxide has received great attention for its catalytic application in water purification. TiO2 catalysts offer a multitude of advantages in AOPs. They are characterized by their high photocatalytic activity under both ultraviolet and visible light, making them environmentally friendly due to the absence of toxic byproducts during oxidation. Their versatility is remarkable, finding utility in various AOPs, from photocatalysis to photo-Fenton processes. TiO2's durability ensures long-lasting catalytic activity, which is crucial for continuous treatment processes, and their cost-effectiveness is particularly advantageous. Furthermore, their chemical stability allows it to withstand varying pH conditions. However, the large band gap energy and low electrical conductivity hinder the catalytic reaction effectiveness. This review aims to examine various approaches to enhance the catalytic performance of titanium dioxide, with the objective of enabling more efficient water purification methods.

Bamboo-Based Biochar: A Still Too Little-Studied Black Gold and Its Current Applications

Biochar (BC), also referred to as "black gold", is a carbon heterogeneous material rich in aromatic systems and minerals, preparable by the thermal decomposition of vegetable and animal biomasses in controlled conditions and with clean technology. Due to its adsorption ability and presence of persistent free radicals (PFRs), BC has demonstrated, among other uses, great potential in the removal of environmental organic and inorganic xenobiotics. Bamboo is an evergreen perennial flowering plant characterized by a short five-year growth period, fast harvesting, and large production in many tropical and subtropical countries worldwide, thus representing an attractive, low-cost, eco-friendly, and renewable bioresource for producing BC. Due to their large surface area and increased porosity, the pyrolyzed derivatives of bamboo, including bamboo biochar (BBC) or activated BBC (ABBC), are considered great bio-adsorbent materials for removing heavy metals, as well as organic and inorganic contaminants from wastewater and soil, thus improving plant growth and production yield. Nowadays, the increasing technological applications of BBC and ABBC also include their employment as energy sources, to catalyze chemical reactions, to develop thermoelectrical devices, as 3D solar vapor-generation devices for water desalination, and as efficient photothermal-conversion devices. Anyway, although it has great potential as an alternative biomass to wood to produce BC, thus paving the way for new bio- and circular economy solutions, the study of bamboo-derived biomasses is still in its infancy. In this context, the main scope of this review was to support an increasing production of BBC and ABBC and to stimulate further studies about their possible applications, thus enlarging the current knowledge about these materials and allowing their more rational, safer, and optimized application. To this end, after having provided background concerning BC, its production methods, and its main applications, we have reviewed and discussed the main studies on BBC and ABBC and their applications reported in recent years.

Petroleum-contaminated soil bioremediation and microbial community succession induced by application of co-pyrolysis biochar amendment: An investigation of performances and mechanisms

This study aimed to remediate petroleum-contaminated soil using co-pyrolysis biochar derived from rice husk and cellulose. Rice husk and cellulose were mixed in various weight ratios (0:1, 1:0, 1:1, 1:3 and 3:1) and pyrolyzed under 500 °C. These biochar variants were labeled as R0C1, R1C0, R1C1, R1C3 and R3C1, respectively. Notably, the specific surface area and carbon content of the co- pyrolysis biochar increased, potentially promoting the growth and colonization of soil microorganisms. On the 60th day, the microbial control group achieved a 46.69% removal of pollutants, while the addition of R0C1, R1C0, R1C3, R1C1 and R3C1 resulted in removals of 70.56%, 67.01%, 67.62%, 68.74% and 67.30%, respectively. In contrast, the highest efficiency observed in the abiotic treatment group was only 24.12%. This suggested that the removal of petroleum pollutants was an outcome of the collaborative influence of co-pyrolysis biochar and soil microorganisms. Furthermore, the abundance of Proteobacteria, renowned for its petroleum degradation capability, obviously increased in the treatment group with the addition of co-pyrolysis biochar. This demonstrated that co-pyrolysis biochar could notably stimulate the growth of functionally associated microorganisms. This research confirmed the promising application of co-pyrolysis biochar in the remediation of petroleum-contaminated soil.

Green Organo-Photooxidative Method for the Degradation of Methylene Blue Dye

This study used an organophoto-oxidative material to degrade the toxic azo dye, methylene blue (MB), due to its hazardous effects on aquatic life and humans. MB is traditionally degraded using metal-based catalysts, resulting in high costs. Several organic acids were screened for organo-photooxidative applications against various azo dyes, and ascorbic acid (AA), also known as vitamin C, was found to be best for degradation due to its high photooxidative activity. It is an eco-friendly, edible, and efficient photooxidative material. A photocatalytic box has been developed for the study of organo-photooxidative activity. It was found that when AA was added, degradation efficiency increased from 42 to 95% within 240 min. Different characterization techniques, such as HPLC and GC-MS, were used after degradation for the structural elucidation of degraded products. DFT study was done for the investigation of the mechanistic study behind the degradation process. A statistical tool, RSM, was used for the optimization of parameters (concentration of dye, catalyst, and time). This study develops sustainable and effective solutions for wastewater treatment.

Research Progress of Ozone/Peroxymonosulfate Advanced Oxidation Technology for Degrading Antibiotics in Drinking Water and Wastewater Effluent: A Review

Nowadays, antibiotics are widely used, increasing the risk of contamination of the water body and further threatening human health. The traditional water treatment process is less efficient in degrading antibiotics, and the advanced oxidation process (AOPs) is cleaner and more efficient than the traditional biochemical degradation process. The combined ozone/peroxymonosulfate (PMS) advanced oxidation process (O3/PMS) based on sulfate radical (SO4•-) and hydroxyl radical (•OH) has developed rapidly in recent years. The O3/PMS process has become one of the most effective ways to treat antibiotic wastewater. The reaction mechanism of O3/PMS was reviewed in this paper, and the research and application progress of the O3/PMS process in the degradation of antibiotics in drinking water and wastewater effluent were evaluated. The operation characteristics and current application range of the process were summarized, which has a certain reference value for further research on O3/PMS process.

Enhanced photocatalytic degradation of methylene blue using a novel counter-rotating disc reactor

Introduction: This research introduces an innovative photocatalytic reactor designed to address challenges in wastewater treatment, with a focus on enhancing dye degradation and reducing Chemical Oxygen Demand (COD). Methods: The reactor is designed with counter-rotational movements of discs to enhance hydrodynamics and mass transfer, along with a 3D-printed, interchangeable component system to boost efficacy. TiO2 nanoparticles, composed of 80% anatase and 20% rutile, are thermally immobilized on glass discs. The effectiveness of various treatment variables was assessed through a Central Composite Design (CCD), guided by a Response Surface Methodology (RSM) model. Results: The RSM analysis reveals that the linear, quadratic, and interactive effects of the counter-rotational movements significantly influence the efficiency of dye and COD removal. The RSM model yields coefficients of determination (R2) values of 0.9758 and 0.9765 for the predictive models of dye and COD removal, respectively. Optimized parameters for dye removal include a pH of 6.05, disc rotation speed of 22.35 rpm, initial dye concentration of 3.15 × 10-5 M, residence time of 7.98 h, and the number of nanoparticle layers set at 3.99, resulting in 96.63% dye removal and 65.81% COD removal under optimal conditions. Discussion: Notably, the reactor demonstrates potential for efficient treatment within a near-neutral pH range, which could reduce costs and resource use by eliminating the need for pH adjustments. The implementation of discs rotating in opposite directions marks a significant advancement in the process of dye removal.

Quantification of the effect of biochar application on heavy metals in paddy systems: Impact, mechanisms and future prospects

Biochar (BC) has shown great potential in remediating heavy metal(loid)s (HMs) contamination in paddy fields. Variation in feedstock sources, pyrolysis temperatures, modification methods, and application rates of BC can result in great changes in its effects on HM bioavailability and bioaccumulation in soil-rice systems and remediation mechanisms. Meanwhile, there is a lack of application guidelines for BC with specific properties and application rates when targeting rice fields contaminated with certain HMs. To elucidate this topic, this review focuses on i) the effects of feedstock type, pyrolysis temperature, and modification method on the properties of BC; ii) the changes in bioavailability and bioaccumulation of HMs in soil-rice systems applying BC with different feedstocks, pyrolysis temperatures, modification methods, and application rates; and iii) exploration of potential remediation mechanisms for applying BC to reduce the mobility and bioaccumulation of HMs in rice field systems. In general, the application of Fe/Mn modified organic waste (OW) derived BC for mid-temperature pyrolysis is still a well-optimized choice for the remediation of HM contamination in rice fields. From the viewpoint of remediation efficiency, the application rate of BC should be appropriately increased to immobilize Cd, Pb, and Cu in rice paddies, while the application rate of BC for immobilizing As should be <2.0 % (w/w). The mechanism of remediation of HM-contaminated rice fields by applying BC is mainly the direct adsorption of HMs by BC in soil pore water and the mediation of soil microenvironmental changes. In addition, the application of Fe/Mn modified BC induced the formation of iron plaque (IP) on the root surface of rice, which reduced the uptake of HM by the plant. Finally, this paper describes the prospects and challenges for the extension of various BCs for the remediation of HM contamination in paddy fields and makes some suggestions for future development.

Amino-grafted Biochar as a Novel Photocatalyst for degradation of high concentration dye

Photocatalytic degradation of organic pollution by biochar was a sustainable strategy for waste water remediation, nevertheless, it still suffers drawbacks like low efficiency due to the poor photocatalytic properties of pristine biochar. Herein, amino groups were grafted on the edge sites/defects of biochar by Friedel-Crafts acylation to enhance the degradation of high concentration dye solutions. The results suggested that the amino groups played an important role in imparting photocatalytic properties to biochar. Owing to the strong Lewis basicity and electron-donating ability of amino groups, their interaction with oxygen-containing functional groups/aromatic structures in biochar was improved, which enhanced the electron exchange ability of biochar under visible light irradiation, resulting in excellent degradation performances of high concentration RhB (∼10 times faster than ungrafted biochar). In this work, amino-grafted garlic peel biochar delivered a new idea for the future direction of biochar-based photocatalysis in wastewater remediation.

Unraveling kinetic and synergistic effects during ultrasound-enhanced carbocatalysis for water remediation as a function of ultrasonic frequency

The ability of the ultrasound (US) combined with peroxymonosulfate (PMS), and a carbonaceous material (BC) was evaluated in the degradation of a model pollutant (acetaminophen, ACE). The US/BC/PMS system was compared with other possible systems (US, oxidation by PMS, BC adsorption, BC/PMS, US/PMS, and US/BC. The effect of the ultrasonic frequency (40, 375, and 1135 kHz) on the kinetics and synergy of the ACE removal was evaluated. In the US system, kinetics was favored at 375 kHz due to the increased production of hydroxyl radicals (HO•), but this did not improve in the US/PMS and US/BC systems. However, synergistic and antagonistic effects were observed at the low and high frequencies where the production of radicals is less efficient but there is an activation of PMS through mechanical effects. US/BC/PMS at 40 kHz was the most efficient system obtaining ∼95% ACE removal (40 μM) in the first 10 min of treatment, and high synergy (S = 10.30). This was promoted by disaggregation of the carbonaceous material, increasing the availability of catalytic sites where PMS is activated. The coexistence of free-radical and non-radical pathways was analyzed. Singlet oxygen (1O2) played the dominant role in degradation, while HO• and sulfate radicals (SO4•-), scarcely generated at low frequency, play a minimum role. Performance in hospital wastewater (HWW), urine, and seawater (SW) evidenced the competition of organic matter by BC active sites and reactive species and the removal enhancement when Cl- is present. Besides, toxicity decreased by ∼20% after treatment, being the system effective after three cycles of reuse.

Recent progress in TiO2-biochar-based photocatalysts for water contaminants treatment: strategies to improve photocatalytic performance

Toxic organic pollutants in wastewater have seriously damaged human health and ecosystems. Photocatalytic degradation is a potential and efficient tactic for wastewater treatment. Among the entire carbon family, biochar has been developed for the adsorption of pollutants due to its large specific surface area, porous skeleton structure, and abundant surface functional groups. Hence, combining adsorption and photocatalytic decomposition, TiO2-biochar photocatalysts have received considerable attention and have been extensively studied. Owing to biochar's adsorption, more active sites and strong interactions between contaminants and photocatalysts can be achieved. The synergistic effect of biochar and TiO2 nanomaterials substantially improves the photocatalytic capacity for pollutant degradation. TiO2-biochar composites have numerous attractive properties and advantages, culminating in infinite applications. This review discusses the characteristics and preparation techniques of biochar, presents in situ and ex situ synthesis approaches of TiO2-biochar nanocomposites, explains the benefits of TiO2-biochar-based compounds for photocatalytic degradation, and emphasizes the strategies for enhancing the photocatalytic efficiency of TiO2-biochar-based photocatalysts. Finally, the main difficulties and future advancements of TiO2-biochar-based photocatalysis are highlighted. The review gives an exhaustive overview of recent progress in TiO2-biochar-based photocatalysts for organic contaminants removal and is expected to encourage the development of robust TiO2-biochar-based photocatalysts for sewage remediation and other environmentally friendly uses.

A critical review of sustainable application of biochar for green remediation: Research uncertainty and future directions

Biochar, a carbon-rich material produced from the pyrolysis of organic biomass, has gained significant attention as a potential solution for sustainable green remediation practices. Several studies analyze biomass-derived biochar techniques and environmental applications, but comprehensive assessments of biochar limitations, uncertainty, and future research directions still need to be improved. This critical review aims to present a comprehensive analysis of biochar's efficacy in environmental applications, including soil, water, and air, by sequentially addressing its preparation, application, and associated challenges. The review begins by delving into the diverse methods of biochar production, highlighting their influence on physical and chemical properties. This review explores the diverse applications of biochar in remediating contaminated soil, water, and air while emphasizing its sustainability and eco-friendly characteristics. The focus is on incorporating biochar as a remediation technique for pollutant removal, sequestration, and soil improvement. The review highlights the promising results obtained from laboratory-scale experiments, field trials, and case studies, showcasing the effectiveness of biochar in mitigating contaminants and restoring ecosystems. The environmental benefits and challenges of biochar production, characterization, and application techniques are critically discussed. The potential synergistic effects of combining biochar with other remediation methods are also explored to enhance its efficacy. A rigorous analysis of the benefits and drawbacks of biochar for diverse environmental applications in terms of technical, environmental, economic, and social issues is required to support the commercialization of biochar for large-scale uses. Finally, future research directions and recommendations are presented to facilitate the development and implementation of biochar-based, sustainable green remediation strategies.

Iron-Cobalt magnetic porous carbon beads activated peroxymonosulfate for enhanced degradation and Microbial inactivation

Magnetic carbon-based catalysts are promising materials for advanced oxidation processes, offering both high catalytic activity and environmental friendliness, and hold great potential in environmental remediation. In this work, Fe and Co zeolite imidazole frameworks (ZIFs) derived micron-sized magnetic porous carbon beads (MPCBs) were prepared by phase inversion and following the carbonization procedure, and the morphological and structural characteristics of the MPCBs were confirmed. The presence of pores and channels in the MPCBs provides a specific microenvironment for the for the catalysis of the core. Bisphenol A (BPA) was selected for the targeted pollutant, and the catalytic experiments confirmed that the effective catalytic activity of MPCBs in the presence of peroxymonosulfate (PMS), which could almost completely degrade BPA in 20 min with a reaction rate of 0.368 min-1. Furthermore, the MPCBs were used to effectively bacterial inactivation. Intermediate products of the BPA degradation process were validated and the toxicological studies showed a gradual decrease in toxicity, indicating effective reduction of potential hazards. The macroscopic preparation methods we developed for MPCBs that is promising for industrial applications and has the potential to cope with complex environmental remediation.

A review of metal-organic framework (MOF) materials as an effective photocatalyst for degradation of organic pollutants

Water plays a vital role in all aspects of life. Recently, water pollution has increased exponentially due to various organic and inorganic pollutants. Organic pollutants are hard to degrade; therefore, cost-effective and sustainable approaches are needed to degrade these pollutants. Organic dyes are the major source of organic pollutants from coloring industries. The photoactive metal-organic frameworks (MOFs) offer an ultimate strategy for constructing photocatalysts to degrade pollutants present in wastewater. Therefore, tuning the metal ions/clusters and organic ligands for the better photocatalytic activity of MOFs is a tremendous approach for wastewater treatment. This review comprehensively reports various MOFs and their composites, especially POM-based MOF composites, for the enhanced photocatalytic degradation of organic pollutants in the aqueous phase. A brief discussion on various theoretical aspects such as density functional theory (DFT) and machine learning (ML) related to MOF and MOF composite-based photocatalysts has been presented. Thus, this article may eventually pave the way for applying different structural features to modulate novel porous materials for enhanced photodegradation properties toward organic pollutants.

Removal of organic pollutants through hydroxyl radical-based advanced oxidation processes

The use of Advance Oxidation Process (AOPs) has been extensively examined in order to eradicate organic pollutants. This review assesses the efficacy of photolysis, O3 based (O3/UV, O3/H2O2, O3/H2O2/UV, H2O2/UV, Fenton, Fenton-like, hetero-system) and sonochemical and electro-oxidative AOPs in this regard. The main purpose of this review and some suggestions for the advancement of AOPs is to facilitate the elimination of toxic organic pollutants. Initially proposed for the purification of drinking water in 1980, AOPs have since been employed for various wastewater treatments. AOPs technologies are essentially a process intensification through the use of hybrid methods for wastewater treatment, which generate large amounts of hydroxyl (•OH) and sulfate (SO4·-) radicals, the ultimate oxidants for the remediation of organic pollutants. This review covers the use of AOPs and ozone or UV treatment in combination to create a powerful method of wastewater treatment. This novel approach has been demonstrated to be highly effective, with the acceleration of the oxidation process through Fenton reaction and photocatalytic oxidation technologies. It is clear that Advance Oxidation Process are a helpful for the degradation of organic toxic compounds. Additionally, other processes such as •OH and SO4·- radical-based oxidation may also arise during AOPs treatment and contribute to the reduction of target organic pollutants. This review summarizes the current development of AOPs treatment of wastewater organic pollutants.

Recent progress in the production and application of biochar and its composite in environmental biodegradation

Over the past few decades, extensive research has been conducted to develop cost-effective and high-quality biochar for environmental biodegradation purposes. Pyrolysis has emerged as a promising method for recovering biochar from biomass and waste materials. This study provides an overview of the current state-of-the-art biochar production technology, including the advancements and biochar applications in organic pollutants remediation, particularly wastewater treatment. Substantial progress has been made in biochar production through advanced thermochemical technologies. Moreover, the review underscores the importance of understanding the kinetics of pollutant degradation using biochar to maximize its synergies for potential environmental biodegradation. Finally, the study identifies the technological gaps and outlines future research advancements in biochar production and its applications for environmental biodegradation.

Z-scheme MnO2/Mn3O4 heterojunctions with efficient peroxymonosulfate activation for organic pollutant removal

The exploration of efficient heterogeneous catalysts for persistent organic pollutant removal is extremely attractive. In the present work, MnO2/Mn3O4 photo-Fenton catalysts were designed by a facile hydrothermal route to activate peroxymonosulfate (PMS) under visible light irradiation for organic pollutant degradation. The optimized MnO2/Mn3O4 heterojunction shows excellent Rhodamine B (RhB) removal efficiency, whose apparent kinetic constant is 11.9 and 5.36 times as high as the MnO2 and Mn3O4. Meanwhile, there is a neglectable attenuation in catalytic performance after 5 recycling runs. Based on the active species trapping experiments, the non-radical process contributes more than the radical process during RhB degradation. Moreover, factors including the dosage of PMS, initial RhB concentration, initial pH, the presence of various anions, different organic pollutants, and water sources are investigated. Systematical characterizations reveal that the enlarged specific surface areas and the efficient charge separation aroused from the Z-scheme mechanism are attributed to the enhanced photo-Fenton performance. The present work contributes to the construction of the Mn-based photo-Fenton catalyst with efficient PMS activation capacity for environmental remediation.

Adsorption and photocatalytic degradation of quinolone antibiotics from wastewater using functionalized biochar

Quinolone antibiotics are emerging environmental contaminants, which cause serious harm to the ecological environment and human health. How to effectively remove these emerging pollutants from water remains a major challenge worldwide. In this study, a novel Fe/Ti biochar composite (Fe/Ti-MBC) was prepared by facile one-step co-pyrolysis of wood chips with hematite and titanium dioxide (TiO2) for adsorption and photocatalytic degradation of ciprofloxacin (CIP) and norfloxacin (NOR) in water. The results showed that the degradation efficiencies of Fe/Ti-MBC to CIP and NOR were 88.4% and 88.0%, respectively. The π-π interactions and polar interactions are the main adsorption mechanisms for CIP and NOR. In the photocatalytic process, h+ and ·OH are the main active substances for the oxidative degradation of CIP and NOR. This study shows that Fe/Ti-MBC is an effective and recyclable composite, providing a novel alternative way for antibiotics degradation.

Enhanced Sorption Performance of Natural Zeolites Modified with pH-Fractionated Humic Acids for the Removal of Methylene Blue from Water

This work explores the effect of humic acids (HA) fractionation on the sorption ability of a natural zeolite (NYT)-HA adduct. HA were extracted from compost, fractionated via the pH fractionation method, and characterized via UV-Vis spectroscopy and gel permeation chromatography. The HA samples were immobilized onto NYT via thermal treatment. The resulting adducts (NYT-HA) were tested for their ability to remove methylene blue (MB) from an aqueous solution. It was found that the sorption performance of NYT-HA strongly depends on the chemical characteristics of humic acids. Sorption capacity increased with the molecular weight and hydrophobicity degree of the HA fractions. Hydrophobic and π-π interactions are likely the primary mechanisms by which MB interacts with HA. The sorption kinetic data conform to the pseudo-second-order model. The Freundlich isotherm model adequately described the sorption equilibrium and revealed that the uptake of MB onto NYT-HA is endothermic in nature.

Characterization and Adsorption Capacity of Modified Biochar for Sulfamethylimidine and Methylene Blue in Water

In this study, a composite of pond mud and lanthanum- and nano-zero valent iron-modified-biochar was investigated for its ability to adsorb methylene blue (MB) and sulfamethazine (SMZ). La-modified attapulgite and nano-zero valent iron (surface area enhanced by 43.7% via Brunauer-Emmett-Teller analysis) were successfully loaded onto the straw-sediment biochar (BC) surface. With the increase in pyrolysis temperature, the biocompatibility yield, the H, O, and N content, and the ratio of carbon elements decreased, while the pH value, surficial micropores, C element, and ash content increased. The biocarbon small molecules were gradually and tightly ordered, and the organic groups such as hydroxyl, carboxyl groups, and carbon oxygen double bonds were gradually lost or disappeared. The original Fe-BC had more phenolic hydroxyl groups forming an intermolecular hydrogen bond than others with a higher adsorption capacity possibly through the Schiff base reaction. The effect of various pH (2-9), temperature (15-35 °C), and initial concentration (1-25 mg L-1) on adsorption was investigated. pH and temperature were the main factors governing the adsorption process. The maximum adsorption capacity was observed at pH 4. The adsorption performances for MB followed the order Fe-BC > La-BC > BC, and the maximum removal rate was over 98.45% with pH = 7. The three types of BC dosages between 0.2 (6.67 g L-1) and 0.4 g showed a removal rate of 99% for MB. The adsorption capacity of Fe-BC, La-BC, and BC for MB was 2.201, 1.905, and 2.401 mg L-1 with pH = 4, while 4.79, 4.58, and 5.55 mg g-1 were observed with BC dosage at 0.025 g. For SMZ, the higher the temperature, the better the adsorption effect, and it reaches saturation at approximately 25 °C. To further evaluate the nature of adsorption, Langmuir/Freundlich/Temkin models were tested and the adsorption capacities were evaluated on the surface of the BC composite. The three modified materials were physisorbed to SMZ, while MB was chemisorbed. For MB, the adsorption performance of BC is the best < 0.2 g (6.67 g L-1) at pH 7.0 at 35 °C. The Elovich model was more suitable for MB, while the Freundlich and Temkin models could better fit the adsorption process of MB. The preparatory secondary dynamics equation and Langmuir equation were more compliant for SMZ, and the saturated adsorption capacities of straw-modified, La-BC, and Fe-BC reached 5.699, 6.088, and 5.678 mg L-1, respectively.

Embedding Hierarchical Pores by Mechanochemistry in Carbonates with Superior Chemoselective Catalysis and Stability

Hierarchical porosity of carbonates can facilitate their performance in massive applications as compared to their corresponding bulk samples. Traditional solution-based precipitation is typically utilized to fabricate porous carbonates. However, this tactic is generally employed under humid conditions, which demand soluble metal precursors, solvents, and extended dry periods. A salt-assisted mechanochemistry is exploited in contemporary work to settle the shortcomings. Enlighted by solid-state technology, this approach eliminates the utilization of solvents, and the process of ball milling can create pores in 5 min. A range of highly porous carbonates and their derivatives are acquired, with several materials surpassing recording surface areas (e.g., H-CaCO3: 108 m2/g, SrCO3: 125 m2/g, BaCO3: 172 m2/g, Pd/H-CaCO3 catalyst: 101 m2/g). The results display that Pd/H-CaCO3 shows superior catalytic efficiency in the synthesis of aniline (turnover frequency [TON] = 1.33 × 104/h-1, yield ≥ 99%, and recycle stability: 11 cycles) and dye degradation. Combining mechanochemistry and salt-assisted tactic provides a facile and efficient pathway for processing porous materials.

Enhanced removal of sulfonamide antibiotics from water by phosphogypsum modified biochar composite

Antibiotic pollution has become a global eco-environmental issue. To reduce sulfonamide antibiotics in water and improve resource utilization of solid wastes, phosphogypsum modified biochar composite (PMBC) was prepared via facile one-step from distillers grains, wood chips, and phosphogypsum. The physicochemical properties of PMBC were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), Zeta potential, X-ray diffraction (XRD), etc. The influencing factors, adsorption behaviors, and mechanisms of sulfadiazine (SD) and sulfamethazine (SMT) onto PMBC were studied by batch and fixed bed column adsorption experiments. The results showed that the removal rates of SD and SMT increased with the increase of phosphogypsum proportion, while decreased with the increase of solution pH. The maximum adsorption capacities of modified distillers grain and wood chips biochars for SD were 2.98 and 4.18 mg/g, and for SMT were 4.40 and 8.91 mg/g, respectively, which was 9.0-22.3 times that of pristine biochar. Fixed bed column results demonstrated that PMBC had good adsorption capacities for SD and SMT. When the solution flow rate was 2.0 mL/min and the dosage of PMBC was 5.0 g, the removal rates of SD and SMT by modified wood chips biochar were both higher than 50% in 4 hr. The main mechanisms of SD and SMT removal by PMBC are hydrogen bonding, π-π donor-acceptor, electrostatic interaction, and hydrophobic interaction. This study provides an effective method for the removal of antibiotics in water and the resource utilization of phosphogypsum.