Electrochemical processes for the treatment of contaminant-rich wastewater: A comprehensive review

Global water demand and environmental concerns related to climate change require industries to develop high-efficiency wastewater treatment methods to remove pollutants. Likewise, toxic pollutants present in wastewater negatively affect the environment and human health, requiring effective treatment. Although conventional treatment processes remove carbon and nutrients, they are insufficient to remove pharmaceuticals, pesticides, and plasticizers. Electrochemical processes effectively remove pollutants from wastewater through the mineralization of non-biodegradable pollutants with consequent conversion into biodegradable compounds. Its advantages include easy operation, versatility, and short reaction time. In this way, this review initially provides a global water scenario with a view to the future. It comprises global demand, treatment methods, and pollution of water resources, addressing various contaminants such as heavy metals, nutrients, organic compounds, and emerging contaminants. Subsequently, the fundamentals of electrochemical treatments are presented as well as electrochemical treatments, highlighting the latest studies involving electrocoagulation, electroflocculation, electroflotation, capacitive deionization and its derivatives, eletrodeionization, and electrochemical advanced oxidation process. Finally, the challenges and perspectives were discussed. In this context, electrochemical processes have proven promising and effective for the treatment of water and wastewater, allowing safe reuse practices and purification with high contaminant removal.

Sediment microbial fuel cell coupled floating treatment wetland for enhancing non-reactive phosphorus removal

The presence of non-reactive phosphorus (NRP) in environmental waters presents a potential risk of eutrophication and poses challenges for the removal of all phosphorus (P) fractions. This study presents the first investigation on the removal performance and mechanism of three model NRP compounds, sodium tripolyphosphate (STPP), adenosine 5'-monophosphate (AMP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), in the sediment microbial fuel cell-floating treatment wetland (SMFC-FTW). Coupling SMFC with plants proved to be effective at removing NRP via electrochemical oxidation and plant uptake, particularly the challenging-to-degrade phosphonates that contain C-P bonds. Compared with the control group, the removal efficiencies of the model NRP in SMFC were observed to increase by 11.9%-20.8%. SMFC promoted the conversion of NRP to soluble reactive phosphorus (sRP) and the transfer of P to sediment. Furthermore, the electrochemical process enhanced both plant growth and P uptake, and increased P assimilation by 72.6%. The presence of plants in the bioelectrochemical system influenced the occurrence and fate of P by efficiently assimilating sRP and supporting microbial transformation of NRP. Consequently, plants enhanced the removal efficiencies of all P fractions in the overlying water. This study demonstrated that SMFC-FTW is a promising technology to remove various NRP species in environmental waters.

Recent advances in electrospinning-nanofiber materials used in advanced oxidation processes for pollutant degradation

Electrospun nanofiber membranes have emerged as a novel catalyst, demonstrating exceptional efficacy in advanced oxidation processes (AOPs) for the degradation of organic pollutants. Their superior performance can be attributed to their substantial specific surface area, high porosity, ease of modification, rapid recovery, and unparalleled chemical stability. This paper aims to comprehensively explore the progressive applications and underlying mechanisms of electrospun nanofibers in AOPs, which include Fenton-like processes, photocatalysis, catalytic ozonation, and persulfate oxidation. A detailed discussion on the mechanism and efficiency of the catalytic process, which is influenced by the primary components of the electrospun catalyst, is presented. Additionally, the paper examines how concentration, viscosity, and molecular weight affect the characteristics of the spinning materials and seeks to provide a thorough understanding of electrospinning technology to enhance water treatment methods. The review proposes that electrospun nanofiber membranes hold significant potential for enhancing water treatment processes using advanced oxidation methods. This is attributed to their advantageous properties and the tunable nature of the electrospinning process, paving the way for advancements in water treatment through AOPs.

Microbial entropy change and external dissipation process of urban sewer ecosystem

As the initial stage of the sewage treatment system, the degradation of pollutants inevitably involves an entropy change process. Microorganisms play a vital role, where they interact with pollutants and constantly adjust own ecosystem. However, there is a lack of research on the entropy change and external dissipation processes within the sewer system. In this study, considering the characteristics of microbial population changes in the biofilm within the urban sewage pipe network, entropy theory is applied to characterize the attributes of different microorganisms. Through revealing the entropy change of the microbial population and chemical composition, a coupling relationship between the functional bacteria diversity, organic substances composition, and external dissipation in the pipeline network is proposed. The results show that the changes of nutrient availability, microbial community structure, and environmental conditions all affect the changes of information entropy in the sewer network. This study is critical for assessing the understanding of ecological dynamics and energy flows within these systems and can help researchers and operation managers develop strategies to optimize wastewater treatment processes, mitigate environmental impacts, and promote sustainable management practices.

Enhanced activation of peroxymonosulfate for advanced oxidation processes using solid waste: A novel and easy implement high-value utilization process of slag

A simple, efficient and low energy-consuming process available to generate resultful radicals from PMS for organic pollutants removal had been employed in this study. Slag had been used as the activator for organic pollutants degradation under slag/PMS advanced oxidation process. In this work, effects of slag with or without pretreatment on pollutant removal were studied and radical species generated by slag were measured. Calcination pretreatment is one efficient method to enhance the degradation efficiency significantly. Due to Fe3O4 and Fe2O3 became the dominant phases after calcination, it was about 8.6-flods increasing after comparing the pollutant removal efficiency for different slag/PMS system with calcination pretreatment or not. Organic pollutant neither degraded in PMS system at 25 °C nor being absorbed by slag system for 60 min. On the contrary, up to 90% pollutant concentration reduction achieved in the slag/PMS process. During this process, both •OH and SO4•- had been detected once slag and PMS interaction in wastewater. Through the free radicals quenching tests,•OH should be the key free radical in this advanced oxidation process for the organic pollutant removal under this alkaline condition. In general, organic degradation rate was determined by the slag dosage, and the maximum degradation efficiency was mainly controlled by the PMS usage. This work is expected to broaden the high-value reutilization way for industrial solid waste.

Synthesis of iron oxide nanoparticles using orange fruit peel extract for efficient remediation of dye pollutant in wastewater

The removal of color-causing compounds from wastewater is a significant challenge that industries encounter due to their toxic, carcinogenic, and harmful properties. Despite the extensive research and development of various techniques with the objective of effectively degrading color pollutants, the challenge still persists. This paper introduces a simple technique for producing iron oxide nanoparticles (Fe2O3 NPs) using orange fruit peel for sustainable dye degradation in aqueous environment. The observation of color change and the measurement of UV-visible absorbance at 240 nm provided a confirmation for the development of Fe2O3 NPs. Transmission electron microscopy examination demonstrated that the Fe2O3 NPs have an agglomerated distribution and forming spherical structures with size ranging from 25-80 nm. Energy-dispersive X-ray spectroscopy analysis supported the existence of Fe and O. Fourier transform infrared spectroscopy conducted to investigate the involvement of orange peel extract in the reduction, capping, and synthesis of Fe2O3 NPs from the precursor salt. Fe2O3 NPs showed a photocatalytic remediation of 97%, for methylene blue under visible light irradiation. Additionally, prepared NPs exhibited concentration depended biofilm inhibition action against E. coli and S. aureus. In conclusion, Fe2O3 NPs can efficiently purify water and suppress pathogens due to their strong degrading activity, reusability, and biofilm inhibition property.

Accelerating the environmental applications of black phosphorus: A review

Since its rediscovery in 2014, layered black phosphorus (BP) has received extensive attention as a new two-dimensional semiconductor. BP is a promising material with properties of a large surface-to-volume ratio, wide light absorption range, tunable band gap, and high charge carrier mobility. These unique characteristics of BP make it a promising contender for various applications, particularly in the realm of environmental applications. This literature review provides a comprehensive discussion and overview of the latest developments in utilizing BP for environmental purposes. The review starts with the applications of BP in photocatalysis including photodegradation of refractory pollutants, H2 evolution reaction (HER), and reduction of CO2 and N2. In the following section, Environmental electrocatalysis of HER and N2 reduction reaction (NRR) is discussed. In addition, BP-based environmental sensing (detection of heavy metal ions, antibiotics, mycotoxins, NOx) and eco-friendly halogen-free flame retardant are summarized as well. Finally, a thorough comprehension of the current state and potential future trends of BP-based nanomaterials for various environmental applications are presented.

Construction of floatable flower-like plasmonic Bi/BiOCl-loaded hollow kapok fiber photocatalyst for efficient degradation of RhB and antibiotics

The development of low-cost and high-efficiency photocatalysts for the degradation of organic pollutants has been an essential and feasible approach to environmental remediation. However, conventional powder photocatalysts suffer from agglomeration, limited light utilization, and reuse difficulties, which hinder their large-scale practical application. Herein, a floatable flower-like plasmonic Bi/BiOCl-loaded hollow kapok fiber (KF/Bi/BC) photocatalyst was synthesized by a facile solvothermal method. It exhibited excellent photocatalytic degradation of Rhodamine B (RhB), ofloxacin (OFX), and tetracycline (TC) under UV-vis irradiation. The incorporation of metallic Bi not only greatly enhanced the light absorption of BiOCl in the visible region but also served as an effective "electron trap", facilitating the efficient separation and transfer of photogenerated electrons and holes. Furthermore, the remarkable floatability of the catalyst contributed to increased light utilization and facilitated the recycling of the catalyst. This work provided a convenient, effective, and feasible method for the fabrication of floatable photocatalysts with excellent catalytic properties, and has great potential for practical applications.

Multimodal energy harvesting and catalysis of piezoelectric nanosheets for efficient and round-the-clock wastewater treatment

Solar-driven pollutants degradation is an important way for green wastewater treatment, but it is still limited by the intermittent solar flux. Here, we have prepared piezoelectric Bi4Ti3O12 (BTO) nanosheets with abundant physical properties, which can convert extensive solar energy, mechanical energy and temperature variation energy into electrical and chemical energy. It can be used for round-the-clock wastewater treatment by harvesting multi-modal energy. More importantly, the degradation rate of piezoelectric nanosheets can reach 153.4 × 10-3 min-1, and nanosheets can degrade many organic pollutants. In addition, we fabricate porous foam catalysts based on BTO-polydimethylsiloxane (PDMS) composite to prevent secondary contamination. Our results suggest that BTO nanosheets with photoelectric, piezoelectric and pyroelectric catalysis offer a potential approach for round-the-clock wastewater degradation by harvesting solar energy, ambient mechanical energy, and cyclic thermal energy.

A novel eco-friendly polymeric photosensitizer based on chitosan and flavin mononucleotide

Flavin mononucleotide (FMN) is a dye belonging to the flavin family. These dyes produce photosensitized degradation of organic compounds via reaction with the excited states of the dye or with reactive oxygen species photogenerated from the triplet of the dye. This article presents a new polymeric dye (FMN-CS) composed of the photosensitizer FMN covalently bonded to chitosan polysaccharide (CS). FMN-CS obtained has a molecular weight of 230 × 103 g mol-1 and a deacetylation degree of 74.8%. The polymeric dye is an environmentally friendly polymer with spectroscopic and physicochemical properties similar to those of FMN and CS, respectively. Moreover, under sunlight, it is capable of generating 1O2 with a quantum yield of 0.31. FMN-CS, like CS, is insoluble in basic media. This allows easy recovery of the polymeric dye once the photosensitized process has been carried out and makes FMN-CS a suitable photosensitizer for the degradation of pollutants in contaminated waters. To evaluate whether FMN-CS may be used for pollutant degradation, the photosensitized degradation of two trihydroxybenzenes by FMN-CS was studied.

Sustainable degradation of pollutants, generation of electricity and hydrogen evolution via photocatalytic fuel cells: An Inclusive Review

Environmental pollution and energy crisis have recently become one of the major global concerns. Insincere discharge of massive amount of organic and inorganic wastes into the aqueous bodies causes serious impact on our environment. However, these organic substances are significant sources of carbon and energy that could be sustainably utilized rather than being discarded. Photocatalytic fuel cell (PFC) is a smart and novel energy conversion device that has the ability to achieve dual benefits: degrading the organic contaminants and simultaneously generating electricity, thereby helping in environmental remediation. This article presents a detailed study of the recent advancements in the development of PFC systems and focuses on the fundamental working principles of PFCs. The degradation of various common organic and inorganic contaminants including dyes and antibiotics with simultaneous power generation and hydrogen evolution has been outlined. The impact of various operational factors on the PFC activity has also been briefly discussed. Moreover, it provides an overview of the design guidelines of the different PFC systems that has been developed recently. It also includes a mention of the materials employed for the construction of the photo electrodes and highlights the major limitations and relevant research scopes that are anticipated to be of interest in the days to come. The review is intended to serve as a handy resource for researchers and budding scientists opting to work in this area of PFC devices.

A microbial flora with superior pollutant removal efficiency and its fermentation process optimization

Microbial flora plays an important role in microorganism-enhanced technology. The pollutant degradation ability and viable counts of these agents are crucial to guarantee their practical application. In this study, an efficient pollutant-degrading microbial flora was screened, its medium components and culture conditions were optimized, and its effect was verified in zeolite trickling filter towers. After a 24 h culture under the optimal conditions, the viable count reached 4.76 × 109 cfu/mL, with the degradation rates of ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N), total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) increased to 93.5%, 100%, 68.3%, 32.6%, and 85%, respectively. After optimizing the feeding strategy, the concentration of viable bacteria reached 5.80 × 109 cfu/mL. In the application effect verification experiment, the degradation rates of NH4+-N, TN, TP, and COD in the experimental group reached 96.69%, 75.18%, 73.82%, and 90.83%, respectively, showing a significant improvement compared to the results of the control group. The main components in the control group were Dokdonella, Brevundimonas, Alishewanella, Rhodobacter, Pseudoxanthomonas, and Thauera, whereas those in the experimental group were Dokdonella, Proteocatella, Rhodobacter, Dechlomonas, and Nitrospira. Proteocatella, Dechlomonas, and Nitrosra, which were unique to the experimental group, are common bacteria used for nitrogen and phosphorus removal. This explains the difference in the sewage treatment capacity between the two groups. This study provides an alternative sewage treatment microbial flora with a reasonable production cost and high degradation efficiency for NH4+-N, TN, TP, and COD.

Enzyme-immobilized hierarchically porous covalent organic framework biocomposite for catalytic degradation of broad-range emerging pollutants in water

Efficient enzyme immobilization is crucial for the successful commercialization of large-scale enzymatic water treatment. However, issues such as lack of high enzyme loading coupled with enzyme leaching present challenges for the widespread adoption of immobilized enzyme systems. The present study describes the development and bioremediation application of an enzyme biocomposite employing a cationic macrocycle-based covalent organic framework (COF) with hierarchical porosity for the immobilization of horseradish peroxidase (HRP). The intrinsic hierarchical porous features of the azacalix[4]arene-based COF (ACA-COF) allowed for a maximum HRP loading capacity of 0.76 mg/mg COF with low enzyme leaching (<5.0 %). The biocomposite, HRP@ACA-COF, exhibited exceptional thermal stability (∼200 % higher relative activity than the free enzyme), and maintained ∼60 % enzyme activity after five cycles. LCMSMS analyses confirmed that the HRP@ACA-COF system was able to achieve > 99 % degradation of seven diverse types of emerging pollutants (2-mercaptobenzothiazole, paracetamol, caffeic acid, methylparaben, furosemide, sulfamethoxazole, and salicylic acid)in under an hour. The described enzyme-COF system offers promise for efficient wastewater bioremediation applications.

Progress on simultaneous photocatalytic degradation of pollutants and production of clean energy: A review

In the current era of severe energy and environmental crises, the need for efficient and sustainable methods to control pollution and promote resource recycling has become increasingly important. Photocatalytic degradation of pollutants and simultaneous production of clean energy is one such approach that has garnered significant attention in recent years. The principle of photocatalysis involves the development of efficient photocatalysts and the efficient utilization of solar energy. The use of organic contaminants can enhance the photocatalytic reactions, leading to the sustainable generation of clean energy. Herein, we provide a comprehensive review of the latest advances in the application of photocatalytic synergized clean energy production in the environmental field. This review highlights the latest developments and achievements in this field, highlighting the potential for this approach to revolutionize the way we approach environmental pollution control and resource recycling. The review focuses on (1) the mechanism of photocatalytic degradation and synergistic energy production, (2) photocatalysts and synthesis strategies, (3) photocatalytic carbon dioxide reduction, (4) pollutant degradation, and (5) hydrogen and electricity production. In addition, perspectives on key challenges and opportunities in photocatalysis and clean energy for future developments are proposed. This review provides a roadmap for future research directions and innovations of photocatalysis that could contribute to the development of more sustainable and cleaner energy solutions.

Recent advancements in MXene-based nanocomposites as photocatalysts for hazardous pollutant degradation - A review

The recent expeditious industrialization and urbanization showcase the increasing need for renewable and non-renewable energy and the severe environmental crisis. In this regard, numerous 2-dimensional (2D) nanomaterials have been developed as a facile approach to meet the futuristic energy essentials and to resolve the crisis. In contrast, the newly explored 2D MXenes (transition metal carbide/nitrides/carbonitride) have been employed as an intriguing material for various environmental applications. This development is accredited to their unique properties, which include a vast surface area, strong electrical conductivity, fascinating photophysical properties, high mechanical properties, stability in an aqueous medium, high hydrophilicity, biocompatibility, ease of functionalization, and excellent thermal properties. MXenes act as a potential candidate in water desalination, energy storage devices such as electrodes of Li-ion batteries and pseudo capacitors, hydrogen production, sensors, and wastewater treatment. This review article deliberates the synthesis of MXene and nanocomposites of MXene and their photo-catalytic actions against various toxic pollutants such as organic dyes and heavy metals in wastewater. This review also precises the various preparation methods of MXene-based photocatalyst and the enhanced photocatalytic activity of MXene and MXene-based nanocomposites in wastewater treatment. Also, it details the attempts made to improve the photocatalytic activity of MXene-based nanocomposites in terms of their structural compositions. In addition, the merits and demerits of the MXene-based photocatalysts are deliberated, which may pave the way for future research in this arena.

Water Vapor Condensation on Iron Minerals Spontaneously Produces Hydroxyl Radical

The hydroxyl radical (^•OH) is a potent oxidant and key reactive species in mediating element cycles and pollutant dynamics in the natural environment. The natural source of ^•OH is historically linked to photochemical processes (e.g., photoactivation of natural organic matter or iron minerals) or redox chemical processes (e.g., reaction of microbe-excreted or reduced iron/natural organic matter/sulfide-released electrons with O₂ in soils and sediments). This study revealed a ubiquitous source of ^•OH production via water vapor condensation on iron mineral surfaces. Distinct ^•OH productions (15-478 nM via water vapor condensation) were observed on all investigated iron minerals of abundant natural occurrence (i.e., goethite, hematite, and magnetite). The spontaneous ^•OH productions were triggered by contact electrification and Fenton-like activation of hydrogen peroxide (H₂O₂) at the water-iron mineral interface. Those ^•OH drove efficient transformation of organic pollutants associated on iron mineral surfaces. After 240 cycles of water vapor condensation and evaporation, bisphenol A and carbamazepine degraded by 25%-100% and 16%-51%, respectively, forming ^•OH-mediated arene/alkene hydroxylation products. Our findings largely broaden the natural source of ^•OH. Given the ubiquitous existence of iron minerals on Earth's surface, those newly discovered ^•OH could play a role in the transformation of pollutants and organic carbon associated with iron mineral surfaces.

Fabrication of novel magnetic Mg0.8Cu0.2Fe2O4/SiO2/CeO2 nanocomposite synthesized by a simple ultrasonic-assisted route for organic dye removal using Fenton-like reaction

Fenton-like degradation of contaminants is considered to be a feasible method for eliminating environmental pollution. In this study, a novel ternary Mg_0.8Cu_0.2Fe₂O₄/SiO₂/CeO₂ nanocomposite was fabricated using a novel ultrasonic-assisted technique, and investigated as a Fenton-like catalyst for the removal of tartrazine (TRZ) dye. The nanocomposite was synthesized by first coating the SiO₂ shell around the Mg_0.8Cu_0.2Fe₂O₄ core via a Stöber-like process to form Mg_0.8Cu_0.2Fe₂O₄/SiO₂. Then, a simple ultrasonic-assisted route was used to synthesize Mg_0.8Cu_0.2Fe₂O₄/SiO₂/CeO₂ nanocomposite. This approach provides a simple and environmentally friendly way to produce this material without the use of any additional reductants or organic surfactants. The fabricated sample demonstrated excellent Fenton-like activity. The efficiency of Mg_0.8Cu_0.2Fe₂O₄ was significantly enhanced by the incorporation of SiO₂ and CeO₂, and complete removal of TRZ (30 mg/L) was achieved within 120 min using 0.2 g/L of Mg_0.8Cu_0.2Fe₂O₄/SiO₂/CeO₂. The scavenger test shows that the main active species is the strong oxidizing of hydroxyl radicals (HO^•). Consequently, the Fenton-like mechanism of Mg_0.8Cu_0.2Fe₂O₄/SiO₂/CeO₂ is explained based on the coexistence of Fe³⁺/Fe²⁺, Cu²⁺/Cu⁺, and Ce⁴⁺/Ce³⁺ redox couples. The removal efficiency of TRZ dye remained around 85% after the third recycling run, revealing that the nanocomposite could be employed to eliminate organic contaminants in water treatment. This research opened up a new avenue for expanding the practical application of new-generation Fenton-like catalysts.

An overview on ZnO-based sonophotocatalytic mitigation of aqueous phase pollutants

Over the past several decades, the increase in industrialization provoked the discharge of harmful pollutants into the environment, affecting human beings and ecosystems. ZnO-based photocatalysts seem to be the most promising photocatalysts for treating harmful pollutants. However, fast charge carrier recombination, photo corrosion, and long reaction time are the significant factors that reduce the photoactivity of ZnO-based photocatalysts. In order to enhance the photoactivity of such photocatalysts, a combined process i.e., sonocatalysis + photocatalysis = sonophotocatalysis was used. Sonophotocatalysis is one of several different AOP methods that have recently drawn considerable interest, as it produces high reactive oxygen species (ROS) which helps in the oxidation of pollutants by acoustic cavitation. This combined technique enhanced the overall efficiency of the individual method by overcoming its limiting factors. The current review aims to present the theoretical and fundamental aspects of sonocatalysis and photocatalysis along with a detailed discussion on the benefits that can be obtained by the combined process i.e., US + UV (sonophotocatalysis). Also, we have provided a comparison of the excellent performance of ZnO to that of the other metal oxides. The purpose of this study is to discuss the literature concerning the potential applications of ZnO-based sonophotocatalysts for the degradation of pollutants i.e., dyes, antibiotics, pesticides, phenols, etc. That are carried out for future developments. The role of the produced ROS under light and ultrasound stimulation and the degradation mechanisms that are based on published literature are also discussed. In the end, future perspectives are suggested, that are helpful in the development of the sonophotocatalysis process for the remediation of wastewater containing various pollutants.

A superior ternary Z-scheme photocatalyst of Bi/Black Phosphorus nanosheets/P-doped BiOCl containing interfacial P-P bond and metallic mediator for H2O2 production and RhB degradation

Photocatalytic performance is significantly influenced by the efficiency of photogenerated electron-hole pairs separation and transfer. In this paper, rational designed Z-scheme Bi/Black Phosphorus Nanosheets/P-doped BiOCl (Bi/BPNs/P-BiOCl) nanoflower photocatalyst was synthesized by a facile in-situ reduction process. The interfacial P-P bond between Black phosphorus nanosheets (BPNs) and P-doped BiOCl (P-BiOCl) was investigated by the XPS spectrum. The Bi/BPNs/P-BiOCl photocatalysts exhibited enhanced photocatalytic performance for H₂O₂ production and RhB degradation. The optimally modified photocatalyst (Bi/BPNs/P-BiOCl-20) showed an excellent photocatalytic H₂O₂ generation rate of 4.92 mM/h and RhB degradation rate of 0.1169 min^-1 under simulated sunlight irradiation, which was 1.79 times and 1.25 times greater than the P-P bond free Bi/BPNs/BiOCl-20. The mechanism was investigated through charge transfer route, radical capture experiments, and band gap structure analysis, indicating that the formation of Z-scheme heterojunctions and interfacial P-P bond not only enhances the redox potential of the photocatalyst but also facilitates the separation and migration of photogenerated electrons-holes. This work might provide a promising strategy for constructing Z-scheme 2D composite photocatalysts combining interfacial heterojunction and elemental doping engineering for efficient photocatalytic H₂O₂ production and organic dye pollutant degradation.

Vivianite-induced peroxymonosulfate activation for containment removal under dark conditions: Performance, mechanism and regeneration

The performance and intrinsic mechanism of vivianite, a natural mineral containing structural Fe(II), for peroxymonosulfate (PMS) activation and pollutant degradation under dark conditions were comprehensively explored in this study. It was found that vivianite was able to efficiently activate PMS to degrade various pharmaceutical pollutants under dark conditions, in which the corresponding reaction rate constant of ciprofloxacin (CIP) degradation was 47- and 32-fold higher than that of magnetite and siderite, respectively. SO₄^·-, ^·OH, Fe(IV) and electron-transfer processes were found in the vivianite-PMS system, while SO₄^·- was the main contributor to CIP degradation. Moreover, mechanistic explorations revealed that the Fe site on the surface of vivianite could bind PMS in the form of a bridge position, and thus vivianite could rapidly activate absorbed PMS due to its strong electron-donating ability. Additionally, it was illustrated that the used vivianite could be efficiently regenerated by either chemical or biological reduction. This study may provide an alternative application of vivianite in addition to phosphorus recovery from wastewater.

Constructing functional metal-organic frameworks by ligand design for environmental applications

Metal-organic frameworks (MOFs) with unique physical and chemical properties are composed of metal ions/clusters and organic ligands, including high porosity, large specific surface area, tunable structure and functionality, which have been widely used in chemical sensing, environmental remediation, and other fields. Organic ligands have a significant impact on the performance of MOFs. Selecting appropriate types, quantities and properties of ligands can well improve the overall performance of MOFs, which is one of the critical issues in the synthesis of MOFs. This article provides a comprehensive review of ligand design strategies for functional MOFs from the number of different types of organic ligands. Single-, dual- and multi-ligand design strategies are systematically presented. The latest advances of these functional MOFs in environmental applications, including pollutant sensing, pollutant separation, and pollutant degradation are further expounded. Furthermore, an outlook section of providing some insights on the future research problems and prospects of functional MOFs is highlighted with the purpose of conquering current restrictions by exploring more innovative approaches.

Investigate the suitability of g-C3N4 nanosheets ornamented with BiOI nanoflowers for photocatalytic dye degradation and PEC water splitting

The two-step thermal polymerization and solvothermal approach is used to construct nano heterostructures of FCN and BiOI (bismuth oxeye iodide), both of which are Nobel metal-free materials. This work reports the effect nano-heterostructure on the micro-structural, light absorption capability, PEC properties and pollutant degradation efficiency of the synthesised heterostructures. The addition to that formation of FCN/BiOI nano-heterostructure enhances the solar light absorption. The FCN/BiOI nano heterostructure shows 10 times higher photocurrent density than the BCN nanostructure and 3.8 time higher that FCN. The FCN/BiOI has a high induced photo-current density (20.17 mA/cm²) and H₂ evolution rate (3762 μmol h^-1 cm^-2) under solar light illumination (λ ≥ 420 nm) in comparison with the other. Furthermore, the photocatalytic performance of this material for the breakdown of methyl red dyes was much greater. Under solar light irradiation, the azo dyes were degraded in 90 min. The FCN/BiOI nano-heterostructure has a higher dye degradation efficiency of 97.91%. The rapid transport of photo-induced electrons in the FCN/BiOI nanocomposite is responsible for the improvement in PEC and PC performances. These impressive findings suggest that this nanocomposite might be used to facilitate the PEC water splitting and the PC degradation of MR in the presence of light. The current research provides insight on how to best tailor composition and structure for efficient FCN photo-electrocatalysis water splitting and Methyl red dye degradation.

Hexagonal-borocarbonitride (h-BCN) based heterostructure photocatalyst for energy and environmental applications: A review

Formulation of heterojunction with remarkable high efficiency by utilizing solar light is promising to synchronously overcome energy and environmental crises. In this concern, hexagonal-borocarbonitride (h-BCN) based Z-schemes have proved potential candidates due to their spatially separated oxidation and reduction sites, robust light-harvesting ability, high charge pair migration and separation, and strong redox ability. H-BCN has emerged as a hotspot in the research field as a metal-free photocatalyst with a tunable bandgap range of 0-5.5 eV. The BCN photocatalyst displayed synergistic benefits of both graphene and boron nitride. Herein, the review demonstrates the current state-of-the-art in the Z-scheme photocatalytic application with a special emphasis on the predominant features of their photoactivity. Initially, fundamental aspects and various synthesis techniques are discussed, including thermal polymerization, template-assisted, and template-free methods. Afterward, the reaction mechanism of direct Z-scheme photocatalysts and indirect Z-scheme (all-solid-state) are highlighted. Moreover, the emerging Step-scheme (S-scheme) systems are briefly deliberated to understand the charge transfer pathway mechanism with an induced internal electric field. This review critically aims to comprehensively summarize the photo-redox applications of various h-BCN-based heterojunction photocatalysts including CO₂ photoreduction, H₂ evolution, and pollutants degradation. Finally, some challenges and future direction of h-BCN-based Z-scheme photocatalyst in environmental remediation are also proposed.

Recent advances in cellulose supported photocatalysis for pollutant mitigation: A review

In recent times, green chemistry or "green world" is a new and effective approach for sustainable environmental remediation. Among all biomaterials, cellulose is a vital material in research and green chemistry. Cellulose is the most commonly used natural biopolymer because of its distinctive and exceptional properties such as reproducibility, cost-effectiveness, biocompatibility, biodegradability, and universality. Generally, coupling cellulose with other nanocomposite materials enhances the properties like porosity and specific surface area. The polymer is environment-friendly, bioresorbable, and sustainable which not only justifies the requirements of a good photocatalyst but boosts the adsorption ability and degradation efficiency of the nanocomposite. Hence, knowing the role of cellulose to enhance photocatalytic activity, the present review is focused on the properties of cellulose and its application in antibiotics, textile dyes, phenol and Cr(VI) reduction, and degradation. The work also highlighted the degradation mechanism of cellulose-based photocatalysts, confirming cellulose's role as a support material to act as a sink and electron mediator, suppressing the charge carrier's recombination rate and enhancing the charge migration ability. The review also covers the latest progressions, leanings, and challenges of cellulose biomaterials-based nanocomposites in the photocatalysis field.

Synthesis of visible light responsive ZnCoFe layered double hydroxide towards enhanced photocatalytic activity in water treatment

In this study, a ternary layered double hydroxide containing Zn, Co, and Fe transition metals (ZnCoFe LDH) was developed using a co-precipitation procedure. The as-synthesized photocatalyst was evaluated for its performance in the degradation of methylene blue (MB) under visible light irradiation. The effects of various process conditions including photocatalyst dosage, pollutant concentration, pH, lamp distance, and lamp power were investigated. The ZnCoFe LDH achieved approximately 74% photodegradation efficiency owing to the narrow bandgap of 2.14 eV. The Langmuir-Hinselwood rate constants were calculated as 1.17 min^-1 and 3.55 min^-1 for photolysis by LED lamp alone and for photocatalysis by LED/ZnCoFe LDH, respectively. The photocatalytic ability of the LDH was attributed to the generation of radical species like ^•OH and O₂^•-. The photocatalytic degradation intermediates of MB were determined by GC-MS analysis. The catalyst retained its performance throughout seven reuse cycles with only a 4.17% reduction in removal efficiency. The energy per order E_EO of the ZnCoFe/LED process in 180 min treatment time was determined as 5.41 kWh.m^-3. order^-1. This study shows that ZnCoFe LDH has sufficient activity and photostability for long-term application in photocatalytic water treatment.

Recent research advancements in microwave photocatalytic treatment of aqueous solutions

In recent years, microwave (MW) photocatalytic treatment was used for the removal of several pollutants from wastewater to overcome the disadvantages of conventional photocatalytic treatment. MW irradiation significantly enhanced the photocatalytic degradation pollutants and is considered an innovative treatment approach. This enhancement in photoactivity was mainly attributed to thermal and non-thermal effects of the MW irradiation. Even though the thermal effects of MW irradiation have been conclusively studied, there are many conflicting results regarding the non-thermal effects in catalysts. In general, it has been verified that the non-thermal effects are due to the electrical and magnetic properties of MW. In this article, a detailed review of the recent advancements in MW-assisted photocatalysis has been done, emphasizing the non-thermal effects of MW radiation on the surface of the catalysts. Also, the evolution of external ultraviolet (UV) sources from the conventional Hg lamp to the latest microwave-driven electrodeless lamps (MDEL) has been discussed. MW photocatalytic treatment using MDELs showed complete removal of lignin, dimethyl phthalate (DMP), and azo dye reactive brilliant red X-3B (BR) and more than 90% removal for cimetidine (CMT), rhodamine B (RB), and methylene blue (MB). A brief comparison regarding the removal efficiencies of pollutants by various AOPs and MW photocatalysis has been made to understand the enhanced photoactivity. In addition, various operating parameters that affect the MW photocatalysis like MW intensity, pH, dissolved oxygen, and catalyst dosage; the degradation pathways of various pollutants; and the cost assessment of MW photocatalysis are discussed in detail. This paper will deliver a scientific and technical overview and useful information to scientists and engineers working in this field.

One-pot synthesis of sodium-doped willow-shaped graphitic carbon nitride for improved photocatalytic activity under visible-light irradiation

Graphitic carbon nitride (g-C₃N₄) is considered as a promising low-cost polymeric semiconductor as conjugated photocatalyst for energy and environmental application. This study exhibits a Na-doped g-C₃N₄ with willow-leaf-shaped structure and high degree of crystallinity, which was synthesized with a convenient thermal polymerization using sodium carbonate (Na₂CO₃) as the sodium source. The π-conjugated systems of g-C₃N₄ were improved by doping sodium, which could accelerate the electron transport efficiency resulting in outstanding photocatalytic properties. Furthermore, optimum Na-doped g-C₃N₄ (CN-0.05) attributed its enhanced irradiation efficiency of light energy to its narrower band gap and significant improvement in charge separation. Consequently, the H₂ evolution rate catalyzed with CN-0.05 can achieve 3559.8 μmol g^-1 h^-1, which is about 1.9 times higher than that with pristine g-C₃N₄. The rate of CN-0.05 for reduction of CO₂ to CO (3.66 μmol g^-1 h^-1) is 6.6 times higher than that of pristine g-C₃N₄. In experiments of pollutants degradation, the reaction constants of degradation of rhodamine B (RhB) and methyl orange (MO) with CN-0.05 were 0.0271 and 0.0101 min^-1, respectively, which are 4.7 and 7.2 times more efficient than pristine g-C₃N₄, respectively. This work provides a simple preparation method for tailoring effective photocatalyst for the sustainable solution of environmental issues.

A new photoelectrochemical cell coupled with the Fenton reaction to remove pollutant and generate electricity under the drive of waste heat

The water and energy crises are becoming increasingly serious with rapid population and economic development. It is urgent to develop new wastewater treatment technologies with high efficiency and low energy consumption. Herein, a solar-salinity nexus cell (called PRC) integrated by a photocatalytic fuel cell and reverse electrodialysis was combined with the Fenton reaction. The PRC-Fenton process can extract electrons from organic wastewater driven by salinity gradient energy for power generation and wastewater remediation in two chambers. The Fenton cathode MOF(2Fe/Co)-GO/GF with good electrocatalytic and photocatalytic activity was developed and optimized in a three-electrode system. GO doping obviously enhanced the catalytic activity and stability of the Fenton cathode. The pollutant (ampicillin, AMP) was simultaneously removed in both anode and cathode chambers of the PRC-Fenton system. AMP removal by the MOF(2Fe/Co)-GO/GF cathode remained above 95% in a wide range of pH values (3.0-7.0). The output current of the PRC-Fenton process was 1.7-2.4 mA. Compared to similar systems, PRC-Fenton is suitable for treating toxic and refractory organic pollutants with green energy in two chambers and generating electricity.

Photoelectrocatalytic activity of highly ordered TiO2 nanotube arrays modified with polyaniline for tetrabromobisphenol A degradation in water

Polyaniline (PANI) is a useful conductive polymer material, and has good adsorption property, which makes it a good modification material. In this work, for the sake of highly enhancing the utilization of visible region in sunlight and accelerating photocatalytic degradation of tetrabromobisphenol A (TBBPA), a typical polybrominated flame retardant, titanium dioxide nanotube arrays (TiO₂ NTAs) were modified with PANI by chemical and electrochemical polymerization. The coated amount of PANI was controlled via adjusting the polymerization time and the amount of aniline in the electrochemical method. The results demonstrate that the EC-PANI/TiO₂ NTAs (synthesized electrochemically) exhibit higher catalytic activity than bare TiO₂ NTAs and C-PANI/TiO₂ NTAs (synthesized chemically) in photoelectrocatalytic degradation of TBBPA under visible light, and the degradation efficiency for TBBPA could reach 94.37% within 120 min. The improved performance was contributed to the synergetic effect of PANI modification which integrated the broad absorption of PANI in visible light region and high catalytic property of TiO₂ NTAs. Interestingly, it was also found that the degradation efficiency of TBBPA by EC-PANI/TiO₂ was further enhanced by up to 95.74% when the ethanol was present in the reaction system as the hole scavenger. Furthermore, the EC-PANI/TiO₂ exhibited excellent stability after 10 cycling experiments. All the results indicated that this new modified material presented strong potential as a photoelectrocatalyst and had great practical applications in the future.

A simple and green method to prepare non-typical yolk/shell nanoreactor with dual-shells and multiple-cores: Enhanced catalytic activity and stability in Fenton-like reaction

Nowadays, non-typical yolk/shell structure has drawn much attentions due to the better catalytic performance than traditional counterparts (one yolk/one shell). In this study, ZIF-67 @Co₂SiO₄/SiO₂ yolk/shell structure was prepared in one-step at room temperature, in which ZIF-67 was served as the hard-template, H₂O was served as etchant and tetraethyl orthosilicat was served as the raw material for Co₂SiO₄/SiO₂. After calcination, the non-typical Co_xO_y @Co₂SiO₄/SiO₂ yolk/shell nanoreactor with Co₂SiO₄/SiO₂ dual-shells and Co_xO_y multiple-cores was obtained. On the one hand, more active sites were exposed on multiple-cores surface and better protection were provided by dual-shells. On the other hand, the sheet-like Co₂SiO₄ inner shell not only extended the travel path and retention time of pollutants trapped in cavity, but also separated the multiple-cores from aggregation. Therefore, the nanoreactor displayed the outstanding catalytic activity and recyclability in Fenton-like reaction. Metronidazole (20 mg/L) was completely degraded after 30 min, rhodamine B (50 mg/L) and methyl orange (20 mg/L) were removed even within 5.0 min. Catalytic mechanism indicated that ¹O₂ greatly contributed to the pollutant degradation. This paper presented a simple, versatile, green and energy-saving method for non-typical yolk/shell nanoreactor, and it could inspire to prepare other catalysts with high activity and stability for environmental remediation.

Degradation of 4-nonylphenol in marine sediments using calcium peroxide activated by water hyacinth (Eichhornia crassipes)-derived biochar

The contamination of marine sediments by 4-nonylphenol (4-NP) has become a global environmental problem, therefore there are necessaries searching appropriate and sustainable remediation methods for in-situ applications. Herein, water hyacinth [(WH) (Eichhornia crassipes)]-derived metal-free biochar (WHBC) prepared at 300-900 °C was used to promote the calcium peroxide (CP)-mediated remediation of 4-NP-contaminaed sediments. At [CP] = 4.37 × 10^-4 M, [WHBC] = 1.5 g L^-1, and pH = 6.0, the degradation of 4-NP was 77% in 12 h following the pseudo-first order rate law with rate constant (k_obs) of 4.2 × 10^-2 h^-1. The efficient 4-NP degradation performance and reaction mechanisms of the WHBC/CP system was ascribed to the synergy between the reactive species (HO• and ¹O₂) at the WHBC surface on which there were abundant electron-rich carbonyl groups and defects/vacancies in the catalyst structure provides active sites, and the ability of the graphitized carbon framework to act as a medium for electron shuttling. According to microbial community analysis based on amplicon sequence variants, bacteria of the genus Solirubrobacter (Actinobacteria phylum) were dominant in WHBC/CP-treated sediments and were responsible for the biodegradation of 4-NP. The results showed great promise and novelty of the hydroxyl radical-driven carbon advanced oxidation processes (HR-CAOPs) that relies on the value-added utilization of water hyacinth for contaminated sediment remediation in achieving circular bioeconomy.

Effectively compound the heterojunction formed by flower-like Bi2S3 and g-C3N4 to enhance photocatalytic activity

In this study, the flower-shaped Bi₂S₃/g-C₃N₄-2.6 heterojunction obtained by solvothermal method and its photocatalytic degradation efficiency of rhodamine B (RhB) and tetracycline (TC) in aqueous solution within 40 min is as high as 98.8% and 94.6%. For RhB degradation, the photocatalytic reaction rate constant (k) of Bi₂S₃/g-C₃N₄-2.6 is approximately 1.8 and 45.5 times that of Bi₂S₃ and g-C₃N₄. For TC, k is 3.1 and 2.4 times that of Bi₂S₃ and g-C₃N₄, respectively. The key to determining the high catalytic activity of Bi₂S₃/g-C₃N₄ lies in the formation of a good heterojunction between Bi₂S₃ and g-C₃N₄, which accelerates the electron transfer rate between the heterojunction interface and effectively avoids electron-hole recombination. The effects of catalyst dosage, different pH values, inorganic anions, and capture agents on the photodegradation performance of RhB were investigated. The results show that the catalyst dosage is 1.33 g/L, and the solution pH is in the range of 5-9, which has the best removal effect on pollutants, and the isolation of holes (h⁺) with strong oxidizing ability promotes the collapse of pollutant molecules. Combined with electrochemical tests, a possible degradation mechanism was advised.

Efficient degradation of organic pollutants by activated peroxymonosulfate over TiO2@C decorated Mg-Fe layered double oxides: Degradation pathways and mechanism

To activate peroxymonosulfate (PMS) is an efficient way for decomposition of non-biodegradable organic pollutants. Herein, Mg-Fe layered double oxides decorated with Ti₃C₂ MXene-derived TiO₂@C (T/LDOs) were fabricated to efficiently activate PMS for the degradation of Rhodamine B (RhB), acid red 1 (AR1), methylene blue (MB), and tetracycline hydrochloride (TC). The T/LDOs catalyst could decompose 95.8% of RhB, 94.8% of AR1, 84.9% of MB within 10 min, and 82.4% of TC within 60 min. The degradation rate constant of RhB in the optimal T/LDOs/PMS system was approximately 2.5 and 15.7 times higher than that in the Mg-Fe LDOs/PMS system and Mg-Fe LDH/PMS system, respectively. Importantly, the T/LDOs exhibited a wide working pH range (3.1-11.0) and high stability with low metal ions leaching, indicating its potential practical applications. Quenching experiments and electronic spin resonance results confirmed that both ^•O₂^- and ¹O₂ were the dominant active species in the T/LDOs/PMS system. In addition, the possible degradation pathway of RhB in the 5%-T/LDOs/PMS system was proposed. Finally, the catalytic mechanism study revealed that the T/LDOs with abundant surface hydroxyl groups and a certain amount of TiO₂@C facilitated the electron transfer between ≡Fe^(Ⅲ)‒OH complex and HSO₅^-, boosting the generation of ^•O₂^- and ¹O₂. This study provides an insight into exploiting highly efficient catalysts for PMS activation towards the degradation of organic pollutants.

Enhanced •OH generation and pollutants removal by framework Cu doped LaAlO3/Al2O3

Highly dispersed framework Cu⁺/Cu²⁺ containing LaAlO₃/Al₂O₃ (La-Cu-Al) was synthesized by a solid-liquid mixed sol-gel method. Excessive Al₂O₃ was confirmed to be necessary for the formation of LaAlO₃. The NMR, EXAFS, FTIR and element mapping results revealed that Cu⁺/Cu²⁺ preferred to substitute octahedral Al sites and bonded by Cu-O-Al in the lattice of LaAlO₃. Compared to La₂CuO₄, CuAl₂O₄ and other reported Fenton-like catalysts, La-Cu-Al was more efficient to mineralize refractory pollutants at a wide pH range of 4.0-10.0. More single electrons around Cu center and octahedral Cu⁺ were confirmed to be responsible for the effective reduction of H₂O₂ into powerful ^•OH. Moreover, organic pollutants as electron donors could interact with surface Cu to accelerate Cu²⁺/Cu⁺ cycle and affect O-O bond of H₂O₂ on La-Cu-Al surface, further promoting the reduction of H₂O₂ into ^•OH. These processes resulted in the high H₂O₂ utilization and the highly efficient removal of pollutants on La-Cu-Al.

Graphitic carbon nitride based immobilized and non-immobilized floating photocatalysts for environmental remediation

In solar photocatalysis, light utilization and recycling of powder from reaction solution are the main obstructions that hinder the photocatalytic efficacy of any photocatalyst. In this respect, a floatable system is effective for efficient solar photocatalysis by light utilization. Due to the maximum solar light absorption property, floating nanocomposite photocatalyst is an appealing substitute for effective wastewater treatment. Floating photocatalysts are a non-oxygenated and non-stirred solution that is a good light harvester, stable, non-toxic, biodegradable, naturally abundant in nature. They also have low density, a simple preparation process, no need to stir, and high porosity. Due to these characteristics, floating photocatalysts are widely favored and ideal candidates for practical environmental remediation. Several researchers have come up with new and innovative ways for immobilizing capable photocatalyst on a floatable substrate to produce floating nanocomposite photocatalytic material. In recent decades, g-C₃N₄-based floating photocatalysts have gained a lot of attention as g-C₃N₄ is a visible light active photocatalyst with unique and exceptional properties. It also has good photocatalytic activity in waste water treatment and environmental remediation. Many previous reports have studied the logical design and manufacturing method for heterojunction floating photocatalysts and immobilized floating photocatalysts. Based on those studies, we have focused on the g-C₃N₄ based immobilized and non-immobilized floating photocatalysts for pollutant degradation. We have also categorized immobilized floating photocatalyst based on several lightweight substrates such as expanded perlite and glass microbead. In addition, future challenges have been discussed to maximize solar light absorption and to improve the efficiency of broadband response floating photocatalysts. Floating photocatalysis is an advanced technique in energy conversion and environmental remediation thus requires special consideration.

Recycling chestnut shell for superior peroxymonosulfate activation in contaminants degradation via the synergistic radical/non-radical mechanisms

The efficient recycling of agricultural chestnut shell waste is of considerable interest due to its large availability and economic feasibility. Herein, an alkaline-activated biochar was thermally prepared using chestnut shell by finely regulating main conditions; its morphological, structural and physic-chemical properties were well characterized. Fenton-like capacity to trigger peroxymonosulfate activation for superior pollutant degradation with high efficiency and good selectivity was validated in different water matrix. Both radical formation and electron transfer were identified as reaction pathways, while the selective non-radical mechanism played the major role in pollutant degradation. Surface ketonic groups were identified as the main reactive sites for non-selective radical production, while crystal edges and structural defects on sp²/sp³ carbon network could smoothly mediate the selective electron transfer from pollutant to oxidant in the non-radical Fenton-like catalysis. The two-mixed radical/non-radical pathways exhibited important advantages for environmental decontamination, in comparison with the one-single radical or non-radical mechanism. Our study provided a promising recycling strategy for agricultural chestnut shell, as well as an environment-friendly catalyst for heterogeneous Fenton-like catalysis in green water purification rendered by the synergistic radical/non-radical reaction pathways.

Application of aluminosilicate clay mineral-based composites in photocatalysis

Aluminosilicate clay mineral (ACM) is a kind of typical raw materials that used widely in manufacturing industry owing to the abundant reserve and low-cost exploring. In past two decades, in-depth understanding on unique layered structure and abundant surface properties endows ACM in the emerging research and application fields. In field of solar-chemical energy conversion, ACM has been widely used to support various semiconductor photocatalysts, forming the composites and achieving efficient conversion of reactants under sunlight irradiation. To date, classic ACM such as kaolinite and montmorillonite, loaded with semiconductor photocatalysts has been widely applied in photocatalysis. This review summaries the recent works on ACM-based composites in photocatalysis. Focusing on the properties of surface and layered structure, we elucidate the different features in the composition with various functional photocatalysts on two typical kinds of ACM, i.e., type 1:1 and type 2:1. Not only large surface area and active surface hydroxyl group assist the substrate adsorption, but also the layered structure provides more space to enlarge the application of ACM-based photocatalysts. Besides, we overview the modifications on ACM from both external surface and the inter-layer space that make the formation of composites more efficiently and boost the photo-chemical process. This review could inspire more upcoming design and synthesis for ACM-based photocatalysts, leading this kind of economic and eco-friendly materials for more practical application in the future.

Perovskite oxide for emerging photo(electro)catalysis in energy and environment

Using solar energy to catalyse photo-driven processes to address the energy crisis and environmental pollution plays a role in the path to a sustainable society. Many oxide-based materials, especially perovskite oxides, have been widely investigated as catalysts for photocatalysis in energy and environment because of the low-cost and earth-abundant and good performance. At this stage, there is a need to present a scientific-based evaluation of the technologies developed so far and identify the most sustainable technologies and the existing limitations and opportunities for their commercialisation. This work comprehensively investigated the outcomes using various scientometric indices on perovskite oxide-based photo(electro)catalysts for water splitting, nitrogen fixation, carbon dioxide conversion, organic pollutant degradation, current trends and advances in the field. According to the results achieved, efforts in both energy and environment based on perovskite oxides have been initiated in the 1990s and accelerated since the 2010s. China and the United States were identified as the most contributing countries. Based on the results achieved in this study, the main milestones and current trends in the development of this field have been identified. The aim of this research is to provide useful guidelines for the further investigation of perovskite oxide-based catalysts for photoelectrocatalysis and photocatalysis both in energy and environment on the applications such as water splitting, nitrogen fixation, carbon dioxide conversion, and wastewater treatment.

Photocatalytic hydrogen evolution by degradation of organic pollutants over quantum dots doped nitrogen carbide

Semiconductor photocatalysts are of great importance for addressing current environmental and energy crises. In this study, we developed a simple exfoliation-sonication route to fabricate nitrogen carbide quantum dots (CNQDs) doped nitrogen carbide nanosheet (CNS) composite photocatalysts which were employed to produce hydrogen and degrade organic pollutants (methyl orange, acridine orange, aniline, and phenol) synchronously under visible light irradiation. The presence of acridine orange and aniline enhanced the hydrogen evolution efficiency from 8.8 mmol g^-1 h^-1 to 32.1 and 11.7 mmol g^-1 h^-1, respectively. On the contrary, methyl orange and phenol with the same concentration inhibited hydrogen evolution. Based on the proton chain and energy band analyses, the synchronous mechanism of photocatalytic hydrogen evolution and organic pollutant degradation on CNQDs/CNS was also proposed. On one side, the oxygen-containing functional groups on the surface of CNQDs and the surrounded water molecules constructed proton chains, increasing the combination probability between protons and photo-generated electrons. On the other side, the heterojunction of CNQDs/CNS induced the separation of photo-generated electron-hole pairs. The photo-generated electrons migrate to CNQDs, on which the protons were transformed into hydrogen molecules, while the holes migrated to CNS where the organic pollutants were oxidized synchronously.

Dibutyl phthalate weakens the role of electroactive biofilm as an efficient wastewater handler and related mechanism

Plasticizer plays an imperceptible role in interfering with the structure and function of wastewater biofilms, but the inherent influence mechanism still remains unknown. Here, the responses in electrochemical, structural, microbial properties of electroactive biofilm (EAB) to plasticizer (dibutyl phthalate, DBP) were comprehensively elucidated, especially for the property variation of extracellular polymeric substances (EPS). The biofilm-0 in DBP-absent environment contributed to 22.9% and 63.9% higher current, compared to those in 1 mg/L and 10 mg/L DBP environment (biofilm-1 and biofilm-10). Chronic exposure to high-concentration DBP significantly boosted the content and distribution width of polysaccharide in EPS, but the electron exchange capacity of EPS decreased 76.6% to 0.146 μmol e^-/mg EPS for biofilm-10. The bacteria were subjected to metabolic function loss, in terms of esterase activity and membrane integrity, by using flow cytometry. The DBP exposure also imposed selective pressure on enrich EPS-secretion-related bacteria, while the Geobacter species decreased from 71.2% (biofilm-0) to 55.8% (biofilm-10). Consequently, the DBP exposure suppressed the pollutant degradation rate, which provided new insights into the EAB role as a promising core for wastewater treatment in plasticizer-existing environments.

Alginate-based nano-adsorbent materials - Bioinspired solution to mitigate hazardous environmental pollutants

Population growth and industrialization is associated with the elevation of hazardous pollutants, including heavy metals, biomedical wastes, personal-care products, endocrine-disrupters, pharmaceutically active compounds, and colorants in the environment. The scientific focus has been devoted to developing novel adsorbents to mitigate hazardous pollutants by constructing hybrids of different polymers and nano-structured materials for improved workability and physicochemical attributes. Recently, much attention has been devoted to nanomaterials in environmental remediation, owning to their exceptional characteristics including novel electrical/chemical features, quantum size effects, tunable functionalization, high scalability, and surface-area-to-volume ratio. Target-specific designing of nanocomposites impart high functionality. The cost-effective and eco-friendly synthesis of bioadsorbent materials is increasing for the removal of hazardous pollutants. Due to biocompatible, biodegradable, and eco-friendly nature, sodium alginate has been widely reported for the preparation of bioadsorbent materials to remove different inorganic/organic pollutants. In this review, the potentialities of alginate-based nanocomposites have been described for environmental remediation purposes. Different nanomaterials, including silica, metallic oxide, graphene oxide, hybrid inorganic-organic, non-magnetic-magnetic, carbon nanorods, nanotubes, polymeric nanocarriers, and several other materials have been described in combination with alginate biopolymer for environmental remediation.

Application of a novel biomimetic double-ligand zirconium-based metal organic framework in environmental restoration and energy conversion

The development of visible-light response photocatalysts with a high catalytic performance and long-term cyclic stability is of great significance in the field of energy and environmental protection. Inspired by photosynthesis, a novel three-dimensional coral zirconium-based metal organic framework (MOF) was synthesized using a double-ligand strategy. The optimal sample, Zr-TCPP-bpydc (2:1), (the ratio of tetra-(4-carboxyphenyl) porphyrin to 2,2'-bipyridine-5,5'-dicarboxylic acid is 2:1) shows an excellent photocatalytic activity under visible light irradiation, and the effects of the amount of photocatalyst, pH and concentration on the degradation rate were investigated under the optimum conditions. It has a high degradation rate of tetracycline (98.12% for tetracycline and 96.74% for ofloxacin), which is 2.11 times higher than that of single ligand Zr-bpydc (zirconium-based MOF containing only 2,2'-bipyridine-5,5'-dicarboxylic acid). More importantly, it also has a good H₂ evolution rate (213.68 μmol g^-1h^-1) and CO₂ reduction (35.81 μmol g^-1h^-1). In addition, the intermediate pathway of degradation, photocatalytic enhancement mechanism and cycle stability were deeply studied by liquid chromatography-mass spectrometry (LC-MS), electron spin resonance spectroscopy (ESR), linear sweep voltammetry (LSV) and recycling tests. The synthesis of a three-dimensional biomimetic coral zirconium-based MOF material will provide guidance for the development of new, promising, and natural ideal photocatalytic materials.

Fabrication of novel Cu2WS4/NiTiO3 heterostructures for efficient visible-light photocatalytichydrogen evolution and pollutant degradation

The design and development of efficient and durable catalysts with visible-light response for photocatalytic hydrogen production and pollutants degradation is considered as one of the most challenging tasks. In present work, a novel Cu₂WS₄/NiTiO₃ (abbreviated as × CWS/NTO; x  = 0.25, 0.50, 0.75 and 1.00) composite was prepared via a facile electrospinning/calcination technique along with a convenient hydrothermal method. The as-prepared CWS/NTOcomposite was composed of 2D CWS nanosheets and 1D NTO nanofibers manifested by SEM and TEM images. The results of XPS verified the interfacial interaction between CWS and NTO, confirming the heterojunction formation in CWS/NTOcomposite. Photocatalytic tests demonstrated as-prepared CWS/NTO catalysts exhibited outstanding and stable photocatalytic performances for H₂ production and pollutants degradation under visible light (λ > 420 nm) irradiation. Specially, 0.50 CWS/NTO sample displayed the highest H₂-evolution activity of 810 μmol·g^-1·h^-1 with the apparent quantum efficiency (AQE) value of 1.65 % at 420 nm. Additionally, it also exhibited the optimal photodegradation properties with the rate constants of 0.030, 0.413 and 0.028 min^-1 for TC, RhB and Cr(VI), respectively. The excellent catalytic activities could be attributed to the enhanced visible-light adsorption, high specific surface area and efficient separation of photogenerated charge carriers. The ESR tests and free radicals capturing experiments confirmed that ·O₂^- and h⁺ were primary active species for TC/RhB degradation. Eventually, the probable catalytic mechanism was put forward and detailly analysed. The present work provides perspectives of rational design on NiTiO₃-based catalysts with superior photocatalytic performance for energy regeneration and environmental remediation.

Effective water/wastewater treatment methodologies for toxic pollutants removal: Processes and applications towards sustainable development

Release of pollutants due to inflating anthropogenic activities has a conspicuous effect on the environment. As water is uniquely vulnerable to pollution, water pollution control has received a considerable attention among the most critical environmental challenges. Diverse sources such as heavy metals, dyes, pathogenic and organic compounds lead to deterioration in water quality. Demand for the pollutant free water has created a greater concern in water treatment technologies. The pollutants can be mitigated through physical, chemical and biological methodologies thereby alleviating the health and environmental effects caused. Diverse technologies for wastewater treatment with an accentuation on pre-treatment of feedstock and post treatment are concisely summed up. Pollutants present in the water can be removed by processes some of which include filtration, reverse osmosis, degasification, sedimentation, flocculation, precipitation and adsorption. Membrane separation and adsorption methodologies utilized to control water pollution and are found to be more effective than conventional methods and established recovery processes. This audit relatively features different methodologies that show remarkable power of eliminating pollutants from wastewater. This review describes recent research development on wastewater treatment and its respective benefits/applications in field scale were discussed. Finally, the difficulties in the enhancement of treatment methodologies for pragmatic commercial application are recognized and the future viewpoints are introduced.

Ce-based heterogeneous catalysts by partial thermal decomposition of Ce-MOFs in activation of peroxymonosulfate for the removal of organic pollutants under visible light

Metal-organic framework (MOF) derivatives have drawn considerable attention for applications in various fields. In this work, spindle-shaped Ce-TCPPs were assembled by a rapid microwave-assisted hydrothermal method. After thermal treatment at low temperature under a N₂ atmosphere, the Ce-TCPPs were partially pyrolyzed and converted to a novel CeO₂/N-doped carbon/Ce-TCPP nanocomposite. Compared to completely decomposed materials, these partially decomposed heterogeneous catalysts exhibited significantly higher photocatalytic activation ability toward PMS for the removal of organic pollutants (e.g., rhodamine B, methylene blue, methyl orange, tetracycline and oxytetracycline). For the optimized sample thermal treated at 450 °C, a 100 mL RhB solution (10 mg/L) can be removed within 20 min with the assistance of PMS under visible light. The significantly enhanced activity can be attributed to the effective spatial separation of photogenerated electrons and holes in the formed Z-scheme CeO₂/N-doped carbon/Ce-TCPP system. This work may provide useful guidance for the design and fabrication of MOF-derived photocatalytic systems for environmental remediation.

Enhanced Fenton-like process via interfacial electron donating of pollutants over in situ Cobalt-doped graphitic carbon nitride

The heterogeneous Fenton process suffers from low efficiency because of the low electron transfer cycle rate of Fe³⁺/Fe²⁺, which often consumes enormous amounts of hydrogen peroxide (H₂O₂) or other energy. Herein, we report a novel Co-based Fenton-like catalyst (in-situ-Co-g-C₃N₄) synthesized via the surface complexation method, in which Co species were modified in situ into the framework of the graphitic carbon nitride (g-C₃N₄) substrate through C-O-Co chemical bonding. The catalyst exhibited higher Fenton-like catalytic activity than pure g-C₃N₄ in the degradation of various pollutants under neutral conditions, as evidenced by the approximately 150-fold higher Fenton-like reaction rate constant of in-situ-Co-g-C₃N₄ than that of g-C₃N₄. Density functional theory (DFT) calculations and a series of experimental and characterization analyses revealed the interfacial reaction mechanism between H₂O₂, pollutants and in-situ-Co-g-C₃N₄. During the Fenton-like reaction, the electron-poor C center on the aromatic ring of g-C₃N₄ could capture the electrons deprived from pollutants, and subsequently deliver them to around the electron-rich Co center to efficiently reduce H₂O₂ to hydroxyl radicals (^•OH), enabling H₂O₂ to be used efficiently for the degradation of pollutants. This study provides a strategy for improving Fenton-like degradation efficiency by effectively utilizing the energy of organic pollutants.

A high-efficiency mediator-free Z-scheme Bi2MoO6/AgI heterojunction with enhanced photocatalytic performance

A high-efficiency Z-scheme Bi₂MoO₆/AgI heterojunction was designed and fabricated via in situ growth of AgI on Bi₂MoO₆. Its photocatalytic activity was investigated with the degradation of malachite green (MG). After 40 min of visible light irradiation, near complete degradation of MG (20 mg/L) occurred when BA11 (Bi₂MoO₆:AgI = 1:1, 2.0 g/L) was present, while only 29.0% and 49.7% of the MG could be degraded in the presence of Bi₂MoO₆ and AgI, respectively. The excellent photocatalytic activity of BA11 results from strong visible light absorption and the low recombination efficiency of photogenerated electron-hole pairs induced by the formation of heterojunction. Density function theory (DFT) calculations revealed that the formation of built-in electric field at the interface between Bi₂MoO₆ and AgI facilitates the effective separation and transfer of photogenerated charge carriers. Results of reuse experiments indicated that the heterostructured photocatalyst has excellent stability. Radical scavenging experiments and electron spin resonance spectra showed that superoxide radicals (O₂^-) and hydroxyl radicals (OH) were the major reactive oxygen species in the photocatalytic system. The photocatalytic degradation pathway of MG was proposed based on the organic degradation intermediates detected. These findings demonstrate that the mediator-free Z-scheme Bi₂MoO₆/AgI heterojunction could serve as a promising photocatalyst in photocatalytic treatment of organic pollutants.

Rate constants of dichloride radical anion reactions with molecules of environmental interest in aqueous solution: a review

Natural waters, water droplets in the air at coastal regions and wastewaters usually contain chloride ions (Cl-) in relatively high concentrations in the milimolar range. In the reactions of highly oxidizing radicals (e.g., •OH, •NO3, or SO4•-) in the nature or during wastewater treatment in advanced oxidation processes the chloride ions easily transform to chlorine containing radicals, such as Cl•, Cl2•-, and ClO•. This transformation basically affects the degradation of organic molecules. In this review about 400 rate constants of the dichloride radical anion (Cl2•-) with about 300 organic molecules is discussed together with the reaction mechanisms. The reactions with phenols, anilines, sulfur compounds (with sulfur atom in lower oxidation state), and molecules with conjugated electron systems are suggested to take place with electron transfer mechanism. The rate constant is high (107-109 M-1 s-1) when the reduction potential the one-electron oxidized species/molecule couple is well below that of the Cl2•-/2Cl- couple.

Responses of electroactive biofilms to chronic chlorine exposure: Insights from the composition and spatial structure of extracellular polymeric substances

Extensive amounts of chlorine disinfectants have been applied to wastewater system since the outbreak of coronavirus disease 2019 (COVID-19), which inevitably affects the pollutant degradation via interfering with electron transfer mediated by electroactive bacteria. Herein, the response of electroactive biofilm (EAB) to chronic chlorine exposure was investigated. Results showed the EAB formed without exposure (EAB-0) exhibited a 53% and 123% higher current output than that formed with 0.1 mg L⁻¹ (EAB-0.1) and 0.5 mg L⁻¹ (EAB-0.5) chlorine, respectively. The chronic chlorine exposure of EAB boosted the contents of extracellular polymeric substances (EPS) in EAB-0.1 and EAB-0.5 by over secretion of extracellular polysaccharides. The EAB-0.1 and EAB-0.5 also presented lower electron exchange capacities (EECs) of EPS, coincided with reduced relative abundance of Geobacter from 61% in EAB-0 to 52% in EAB-0.5. This study provided new insights into the application of engineered EAB for wastewater treatment in a disinfection environment.

BiO(OH)xI1-x solid solution with rich oxygen vacancies: interlayer guest hydroxyl for improved photocatalytic properties

A series of BiO(OH)_xI_1-x solid solution (SS) catalysts were successfully prepared by ion exchange of I^- and OH^- between the [Bi₂O₂]²⁺ layers. The morphology and microstructure were studied in depth using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Brunauer-Emmett-Teller (BET) method, etc. Tunable absorption in the visible-light region was achieved by changing the proportion of OH^- to I^-. Due to the etching effect of OH^-, oxygen vacancies (OVs) greatly increased for the SS catalysts, and were confirmed by X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), and electron paramagnetic spectroscopy (EPR). The unique composition of OH^-, I^-, OV, and [Bi₂O₂]²⁺ layers in BiO(OH)_xI_1-x materials resulted in diverse photoexcitations. The BiO(OH)_0.45I_0.55 photocatalyst displayed a 10-fold-improved 2-chlorophenol (2-CP) degradation rate compared to BiOI. The interfacial reaction process by the photoinduced valence-band holes and conduction-band electrons proved to be a more efficient pathway for organic pollutant degradation by the BiO(OH)_xI_1-x SS photocatalyst. The OVs in the SS photocatalyst facilitated photoexcited and electron migration and transformation.