Base Catalytic Approach: A Promising Technique for the Activation of Biochar for Equilibrium Sorption Studies of Copper, Cu(II) Ions in Single Solute System

Mathematical Modelling and Optimization for Facile Synthesis of Structured Activated Carbon (ACs) from Adansonia kilima (Baobab) Wood Chips Integrating Microwave-Assisted Pyrolysis for the Elimination of Lead (II) Cations from Wastewater Effluents

In this research, activated carbon (AC) was synthesized from ligno-cellulosic residues of Adansonia kilima (Baobab) wood chips (AKTW) using two-step semi-carbonization and subsequent pyrolysis using microwave-induced heating (MWP) in the presence of a mild activating agent of K2CO3. The influence of process input variables of microwave power (x1), residence time (y1), and amount of K2CO3 (z1) were analysed to yield superior quality carbon having maximum removal efficiencies (R1) for lead (II) cations from waste effluents, fixed carbon percentages (R2), and carbon yield percentages (R3). Analysis of variance (ANOVA) was used to develop relevant mathematical models, with an appropriate statistical assessment of errors. Level factorial response surface methodology (RSM) relying on the Box-Behnken design (BBD) was implemented for the experimental design. The surface area and porous texture of the samples were determined using Brunauer, Emmett, and Teller (BET) adsorption/desorption curves based on the N2 isotherm. Surface morphological structure was observed using field emission scanning electron microscopic (FESEM) analysis. Thermogravimetric analysis (TGA) was carried out to observe the thermal stability of the sample. Change in the carbon content of the samples was determined using ultimate analysis. X-ray diffraction (XRD) analysis was performed to observe the crystalline and amorphous texture of the samples. The retention of a higher proportion of fixed carbon (80.01%) ensures that the synthesized adsorbent (AKTWAC) will have a greater adsorption capacity while avoiding unwanted catalytic activity for our synthesized final sample.

The role of anthocyanin and kaolinite in modifying cabbage leaves biochar for removal of potentially toxic elements and pharmaceutical from aqueous solution

We investigated the feasibility of two novel engineered biochar composites by pyrolyzing cabbage leaves at 350 °C after pre-treating them with anthocyanin, followed by a post-treatment with kaolinite for the removal of two potentially toxic elements (copper and lead) and a pharmaceutical compound, metoprolol. Results showed that the Kaolinite-biochar composite (KB) exhibited the highest adsorption capacity, 188.67 and 48.07 mg/g for Pb and Cu at pH 5, and the anthocyanin-biochar composite (AB) exhibited the highest adsorption capacity: 41.15 mg/g for metoprolol at pH 6, compared to raw biochar respectively. The enhancement of the adsorption of heavy metal and metoprolol by KB and AB was due to an increase in certain oxygen functional groups, as confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) results. The pseudo-second order kinetic model, along with Langmuir isotherm model, best described the kinetic and the isotherms for Pb, Cu and metoprolol in KB and AB composites, respectively. FTIR, XPS, and zeta potential measurements indicated that the sorption mechanisms involved electrostatic interaction, ion exchange, and complexation for the metals, while electrostatic interaction, H-bonding, π-πinteraction, and hydrophobic bonding were postulated as the contributing mechanisms in the sorption process of metoprolol. Anthocyanin and kaolinite could potentially be considered as alternative sustainable materials for modifying raw biochar and remediating toxic elements and pharmaceuticals in aqueous media.

Study of synthesis and characterization of raw bagasse, its char and activated carbon prepared using chemical additive

This paper reports the use of naturally available raw material as sugarcane bagasse (SB) to prepare cost-effective activated carbon. Activated carbon preparation from SB by using ZnCl₂ was carried out by chemical activation method. The raw bagasse, its char and activated carbon were characterized on the basis of iodine number, carbon, hydrogen, nitrogen analysis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) surface area to check their effectiveness. During activated carbon synthesis, the impregnation ratio of SB and ZnCl₂ was maintained at 1:1-1:3 and activation temperature was in the range of 600-900 °C for 1 h. From the characterization study, the highest iodine adsorption of activated carbon was found to be 1140.69 mg/g with a 1:2 ratio at 900 °C whereas char gives an iodine number of 529.63 mg/g at the same temperature. The BET surface area of raw bagasse, its char and activated carbon (SB-Zn₂-900) obtained was 4.30, 514.27 and 1386.58 m²/g, respectively, which shows charrification and chemical activation improves surface area. The optimum ratio of impregnation and activation temperature was found to be 1:2 at 900 °C. In this work, activated carbon was successfully prepared and obtained product has better characteristics than previously reported studies.

Silicon modification improves biochar's ability to mitigate cadmium toxicity in tomato by enhancing root colonization of plant-beneficial bacteria

Modification of biochar, such as impregnation with minerals, can improve biochar's efficacy to mitigate heavy metal toxicity in plants. Biochar amendments can alter plant rhizosphere microbiome, which has profound effects on plant growth and fitness. Here, we tested whether rhizosphere microbiome is involved in the ability of silicon (Si)-modified biochar to mitigate cadmium toxicity in tomato (Solanum lycopersicum L.). We demonstrated that Si modification altered biochar's physico-chemical properties and enhanced its ability to mitigate cadmium toxicity in tomato. Particularly, the Si-modified biochar contained higher content of Si and increased plant-available Si content in the soil. The rhizosphere microbiome transplant experiment showed that changes in rhizosphere microbiome contributed to the mitigation of cadmium toxicity by biochar amendments. The raw biochar and Si-modified biochar differently altered tomato rhizosphere bacterial community composition. Both biochars, especially the Si-modified biochar, promoted specific bacterial taxa (e.g., Sphingomonas, Lysobacter and Pseudomonas spp.). Subsequent culturing found these promoted bacteria could mitigate cadmium toxicity in tomato. Moreover, both biochars stimulated tomato to recruit plant-beneficial bacteria with Si-modified biochar having stronger stimulatory effects, indicating that the positive effects of biochar on plant-beneficial bacteria was partially mediated via the host plant. Overall, Si modification enhanced biochar's ability to mitigate cadmium toxicity, which was linked to the stimulatory effects on plant-beneficial bacteria.

Efficient removal of pefloxacin from aqueous solution by acid-alkali modified sludge-based biochar: adsorption kinetics, isotherm, thermodynamics, and mechanism

In this paper, one kind of acid-alkali modified sludge-based biochar (ASBC) was synthesized, characterized, and employed as adsorbent for the removal of pefloxacin. The characterization results showed that the specific surface area (SSA) of ASBC (53.381 m²/g) was significantly higher than that of SBC (24.411 m²/g). ASBC had a rougher surface, larger particle distribution, lower zero point charge, and richer functional groups (e.g., C-O and O-H) than SBC. The adsorption capacity of ASBC was 1.82 times than that of SBC. After 8 adsorption cycles in reuse experiment, the adsorption capacity of ASBC for pefloxacin still reached 144.08 mg/L, indicating that ASBC has good reusability. Static experiments showed that the optimal pH value was 6.0 in the adsorption of pefloxacin on SBC and ASBC. The result of adsorption kinetics indicated that the pseudo-second-order model could describe well the adsorption process. The Freundlich model was better than the Langmuir model to describe the adsorption of pefloxacin by ASBC, indicating that the adsorption process was mainly multilayer adsorption. Thermodynamic result showed that the adsorption of pefloxacin by ASBC was spontaneous and endothermic. The removal mechanism of pefloxacin by ASBC is mainly the substitution reaction and π-π EDA interaction. In summary, acid-alkali modified biochar is an effective adsorbent for pefloxacin in aqueous solution, and has great application prospects.

Adsorption Studies of Volatile Organic Compound (Naphthalene) from Aqueous Effluents: Chemical Activation Process Using Weak Lewis Acid, Equilibrium Kinetics and Isotherm Modelling

This study deals with the preparation of activated carbon (CDSP) from date seed powder (DSP) by chemical activation to eliminate polyaromatic hydrocarbon-PAHs (naphthalene-C₁₀H₈) from synthetic wastewater. The chemical activation process was carried out using a weak Lewis acid of zinc acetate dihydrate salt (Zn(CH₃CO₂)₂·2H₂O). The equilibrium isotherm and kinetics analysis was carried out using DSP and CDSP samples, and their performances were compared for the removal of a volatile organic compound-naphthalene (C₁₀H₈)-from synthetic aqueous effluents or wastewater. The equilibrium isotherm data was analyzed using the linear regression model of the Langmuir, Freundlich and Temkin equations. The R² values for the Langmuir isotherm were 0.93 and 0.99 for naphthalene (C₁₀H₈) adsorption using DSP and CDSP, respectively. CDSP showed a higher equilibrium sorption capacity (q_e) of 379.64 µg/g. DSP had an equilibrium sorption capacity of 369.06 µg/g for C₁₀H₈. The rate of reaction was estimated for C₁₀H₈ adsorption using a pseudo-first order, pseudo-second order and Elovich kinetic equation. The reaction mechanism for both the sorbents (CDSP and DSP) was studied using the intraparticle diffusion model. The equilibrium data was well-fitted with the pseudo-second order kinetics model showing the chemisorption nature of the equilibrium system. CDSP showed a higher sorption performance than DSP due to its higher BET surface area and carbon content. Physiochemical characterizations of the DSP and CDSP samples were carried out using the BET surface area analysis, Fourier-scanning microscopic analysis (FSEM), energy-dispersive X-ray (EDX) analysis and Fourier-transform spectroscopic analysis (FTIR). A thermogravimetric and ultimate analysis was also carried out to determine the carbon content in both the sorbents (DSP and CDSP) here. This study confirms the potential of DSP and CDSP to remove C₁₀H₈ from lab-scale synthetic wastewater.

Application of biochar in advanced oxidation processes: supportive, adsorptive, and catalytic role

The advanced oxidation processes (AOPs), especially sulphate radical (SO₄^•-)-based AOPs (SR-AOPs), have been considered more effective, selective, and prominent technologies for the removal of highly toxic emerging contaminants (ECs) due to wide operational pH range and relatively higher oxidation potential (2.5-3.1 V). Recently, biochar (BC)-based composite materials have been introduced in AOPs due to the dual benefits of adsorption and catalytic degradation, but the scientific review of BC-based catalysts for the generation of reactive oxygen species (ROSs) through radical- and non-radical-oriented routes for EC removal was rarely reported. The chemical treatments, such as acid/base treatment, chemical oxidation, surfactant incorporation, and coating and impregnation of minerals, were applied to make BC suitable as supporting materials (SMs) for the loading of Fenton catalysts to boost up peroxymonosulphate/persulphate/H₂O₂ activation to get ROSs including ^•OH, SO₄^•-, ¹O₂, and O₂^•- for targeted pollutant degradation. In this review, all the possible merits of BC-based catalysts including supportive, adsorptive, and catalytic role are summarised along with the possible route for the development prospects of BC properties. The limitations of SR-AOPs especially on production of non-desired oxyanions, as well as disinfection intermediates and their potential solutions, have been identified. Lastly, the knowledge gap and future-oriented research needs are highlighted.

Recent advances in biochar application for water and wastewater treatment: a review

In the past decade, researchers have carried out a massive amount of research on the application of biochar for contaminants removal from aqueous solutions. As an emerging sorbent with great potential, biochar has shown significant advantages such as the broad sources of feedstocks, easy preparation process, and favorable surface and structural properties. This review provides an overview of recent advances in biochar application in water and wastewater treatment, including a brief discussion of the involved sorption mechanisms of contaminants removal, as well as the biochar modification methods. Furthermore, environmental concerns of biochar that need to be paid attention to and future research directions are put forward to promote the further application of biochar in practical water and wastewater treatment.

Synthesis, characterization and application of magnetic and acid modified biochars following alkaline pretreatment of rice and cotton straws

The development of distinct biochar from agricultural waste for soil and environment remediation is valuable. Moderate pretreatment with sodium hydroxide may open the lignocellulosic structure of crop straw and then enhance the impregnation of iron oxides and phosphates, finally leading to the production of distinct biochars. In this study, two common agricultural wastes of rice and cotton straw were first treated with a dilute NaOH solution and then soaked in either Fe-Co nitrate or H₃PO₄ solution. The biochars produced through a slow pyrolysis process were then analyzed with respect to their physico-chemical and adsorptive properties. The results showed that all pretreatments remarkably changed the physico-chemical properties of the feedstocks and subsequently endowed the biochars with distinct characteristics. The biochars had specific surface areas (SSAs) ranging from 12.26 to 581.13 m²/g, total pore volumes (TPVs) ranging from 0.033 to 0.3736 cm³/g and average pore volumes (APSs) ranging from 2.57 to 10.76 nm. They also contained a large amount of positive charge, an anion exchange capacity (pH 3.5) ranging from 251.78 to 810.13 mmol/kg, and a certain amount of negative charge as well, cation exchange capacity (pH 7.0) ranging from 108.22 to 464.67 mmol/kg. The adsorption capacities of the modified biochars toward both Pb²⁺ and Cd²⁺ were 23.07-82.74% and 16.90-556.33% higher than those of pristine biochars, respectively. Of the modified biochars, the Fe-Co-composite biochar showed many promising physico-chemical and adsorptive properties for adsorbing divalent metals of both Pb²⁺ and Cd²⁺ and might thus have high potential as a soil amendment and an alternative adsorbent for environmental remediation.

Production of activated carbons from four wastes via one-step activation and their applications in Pb2+ adsorption: Insight of ash content

Natural biomass is a renewable source for precursors of porous carbon. Four agriculture wastes of corn cob (CC), wheat bran (WB), rice husk (RH), and soybean shell (SS) were applied to produce activated carbons (ACs) via one-step activation by sodium hydroxide. The effects of ash contents and NaOH dosage ratio (1-5) on surface area for ACs were investigated. Owing to ash etching, the high ash precursor (like RH) exhibited less alkali consumption and larger surface area than low ash one (like CC). All four ACs expressed developed pore structure and outstanding surface area of ∼2500 m²g^-1. During adsorption of lead ions in simulated wastewater, RH-based AC revealed superior capture capacity of 492 ± 15 mgg^-1. One-step activation had the potential to deliver savings around 1/3 of energy consumption, enabling the cost performance of high ash RH-based AC reaching 194 ± 12 g Pb²⁺$^-1, 76% larger than low ash CC-based AC. High ash biomass is a promising candidate to obtain eco-friendly carbon products.

The inappropriate application of the regression Langmuir Qm for adsorption capacity comparison

The Langmuir equation, the best known adsorption model in the past century, was extensively applied to describe adsorption isotherms. The saturated adsorption amount (Q_m) obtained from the Langmuir model is an essential index to evaluate the maximum adsorption capacity of the adsorbent, which was assumed to be irrelevant to the aqueous concentration of the adsorbate. Adsorption isotherms of cadmium onto soil and biochar were performed in the current study, and the regression Langmuir Q_m was demonstrated to be highly dependent on the aqueous concentration. The regression Q_m increased from 0.066 to 2.17 mg·g^-1 (by ~3-fold) for the selected soil, and from 2.12 to 48.4 mg·g^-1 (by ~23-fold) for the chosen biochar when the highest initial aqueous concentration increased from 2.34 to 887 mg·L^-1. One inappropriate application for comparison of the regression Langmuir Q_m as the adsorption capacity is found, i.e., it is difficult to directly compare the regression Q_m without neither a saturated isotherm nor considering the experimental conditions. It is also very hard to accurately predict adsorption behavior by the regressed Langmuir model obtained from a partial adsorption isotherm. It is suggested to pay more attention to the difference between the saturated adsorption capacity and the regression Q_m value derived from one unsaturated isotherm.

A review of biochar-based sorbents for separation of heavy metals from water

Biochar is the low-cost and environmental-friendly material which has shown a great potential for separation of heavy metals from water. The previous studies have established a superior role of biochar over other materials, such as activated carbon and inorganic sorbents (iron based) in efficient removal of toxic heavy metals from aqueous systems. Among the various factors influencing heavy metals sorption ability of biochar, types of feedstock/biomass and pyrolysis temperature play a significant role. The goal of this review is to increase our understanding of heavy metals sorption behavior by biochars - this is important as heavy metals sorption is driven based on biochar type, heavy metals species which involve numerous mechanisms, including the physical binding, complexation, ion exchange, surface precipitation and electrostatic interactions. In addition, this review paper describes various approaches to improve heavy metal sorption capacity of biochars by steam and acids/bases activations and impregnation of biochar-based composites with minerals, organic compounds and carbon-rich materials. The physical/chemical activation of biochars can improve the surface area, thus leading to their improved functionality, while modification/pretreatment methods help in synthesizing composites using biochar as a supporting media to develop new sorbents with efficient surface attributes for heavy metals removal from aqueous solutions.

Aged microplastics polyvinyl chloride interact with copper and cause oxidative stress towards microalgae Chlorella vulgaris

Microplastics (MPs) could pose potential risks to microalgae, the primary producer of marine ecosystems. Currently, few studies focus on the interaction of aged MPs with other pollutants and their toxic effects to microalgae. Therefore, the present study aimed to investigate i) the aging of microplastics polyvinyl chloride (mPVC) in simulated seawater and the changes in physical and chemical properties; ii) the effects of single mPVC (virgin and aged) and copper on microalgae Chlorella vulgaris; and iii) the interaction of aged mPVC and copper and the oxidative stress towards C. vulgaris. In this study, some wrinkles, rough and fractured surface textures can be observed on the aged mPVC, accompanying with increased hydroxyl groups and aromatic carbon-carbon double bond but decreased carbon hydrogen bond. It was found that single virgin or aged mPVC at low concentration (10 mg/L) had significant inhibition on the growth of C. vulgaris but no inhibition at higher concentration (100, 1,000 mg/L), which can be reasonably explained by the aggregation and precipitation of mPVC at high concentration. The aging of mPVC inhibited the growth of C. vulgaris with the maximum growth inhibition ratio (IR) of 35.26% as compared with that of virgin mPVC (IR = 28.5%). However, the single copper could significantly inhibit the growth of C. vulgaris and the inhibitory effects increased with concentration (0.2, 0.5, 1.0 mg/L). Furthermore, both the single aged mPVC (10 mg/L) and copper (0.5 mg/L) caused serious cell damage, although the concentration of superoxide dismutase (SOD) and the intracellular malonaldehyde (MDA) increased. In contrast to single treatment, the growth of C. vulgaris can be enhanced by the combined group with copper (0.5 mg/L) and aged mPVC (10 mg/L).

Urea functionalization of ultrasound-treated biochar: A feasible strategy for enhancing heavy metal adsorption capacity

The main objective of a series of our researches is to develop a novel acoustic-based method for activation of biochar. This study investigates the capability of biochar in adsorbing Ni(II) as a hazardous contaminant and aims at enhancing its adsorption capacity by the addition of extra nitrogen and most probably phosphorous and oxygen containing sites using an ultrasono-chemical modification mechanism. To reach this objective, biochar physically modified by low-frequency ultrasound waves (USB) was chemically treated by phosphoric acid (H₃PO₄) and then functionalized by urea (CO(NH₂)₂). Cavitation induced by ultrasound waves exfoliates and breaks apart the regular shape of graphitic oxide layers of biochar, cleans smooth surfaces, and increases the porosity and permeability of biochar's carbonaceous structure. These phenomena synergistically combined with urea functionalization to attach the amine groups onto the biochar surface and remarkably increased the adsorption of Ni(II). It was found that the modified biochar could remove > 99% of 100 mg Ni(II)/L in only six hours, while the raw biochar removed only 73.5% of Ni(II) in twelve hours. It should be noted that physical treatment of biochar with ultrasound energy, which can be applied at room temperature for a very short duration, followed by chemical functionalization is an economical and efficient method of biochar modification compared with traditional methods, which are usually applied in a very severe temperature (>873 K) for a long duration. Such modified biochars can help protect human health from metal-ion corrosion of degrading piping in cities with aging infrastructure.

Chemical activation of biochar for energy and environmental applications: a comprehensive review

Biochar (BC) generated from thermal and hydrothermal cracking of biomass is a carbon-rich product with the microporous structure. The graphene-like structure of BC contains different chemical functional groups (e.g. phenolic, carboxylic, carbonylic, etc.), making it a very attractive tool for wastewater treatment, CO2 capture, toxic gas adsorption, soil amendment, supercapacitors, catalytic applications, etc. However, the carbonaceous and mineral structure of BC has a potential to accept more favorable functional groups and discard undesirable groups through different chemical processes. The current review aims at providing a comprehensive overview on different chemical modification mechanisms and exploring their effects on BC physicochemical properties, functionalities, and applications. To reach these objectives, the processes of oxidation (using either acidic or alkaline oxidizing agents), amination, sulfonation, metal oxide impregnation, and magnetization are investigated and compared. The nature of precursor materials, modification preparatory/conditions, and post-modification processes as the key factors which influence the final product properties are considered in detail; however, the focus is dedicated to the most common methods and those with technological importance.

Porous nano-cerium oxide wood chip biochar composites for aqueous levofloxacin removal and sorption mechanism insights

The adsorption removal of levofloxacin (LEV), a widely used fluoroquinolone antibiotic, by using the biochars derived from the pyrolysis of pine wood chip pretreated with cerium trichloride was investigated through batch sorption experiments and multiple characterization techniques. The differences in the basic physicochemical properties between Ce-impregnated biochars and the pristine biochars were confirmed by the analysis of elemental compositions, specific surface areas, energy dispersive spectrometry, X-ray diffraction, and thermo-gravimetry. FT-IR spectra of the pre- and post-sorption biochars confirmed the chemical adsorption for LEV sorption onto the biochars. Large shifts in the binding energy of Ce_3d, O_1s, C_1s, and N_1s regions on the pre- and post-sorption biochars indicated the surface complexation of LEV molecule onto the biochars. The binding species of Ce⁴⁺ and Ce³⁺ identified by X-ray photoelectron spectroscopy reflect the role of Ce oxides during sorption. Batch adsorption showed the significant enhancement of adsorption capacity for LEV after the Ce modification. Batch adsorption kinetic data fitted well with the pseudo-second-order model. Both the Langmuir and the Freundlich models reproduced the isotherm data well. Findings from this work indicated that Ce-impregnated biochars can be effective for the removal of aqueous LEV.

Effect of Temperature on the Physical, Electro-Chemical and Adsorption Properties of Carbon Micro-Spheres Using Hydrothermal Carbonization Process

This research deals with the effect of the temperature on the physical, thermal, electrochemical, and adsorption properties of the carbon micro-spheres using hydrothermal carbonization (HTC). Until recently, limited research has been conducted regarding the effects of delignification during the HTC process of biomass residues especially Dimocarpus longan. In this regard, lignin was first extracted from the lingo-cellulosic waste of Longan fruit peel (Dimocarpus longan). The holocellulose (HC) separated from lignin and raw biomass substrates (Longan fruit exocarp/peel powder, LFP) were carbonized at different temperatures using water as the green catalyst. Hydrothermal carbonization (HTC) was performed for both of the samples (LFP and HC) at 200 °C, 250 °C, and 300 °C for 24 h each. The surface morphological structures, the porosity, and the Brunauer-Emmett-Teller (BET) surface area of the prepared micro-spherical carbon were determined. The BET surface areas obtained for HC-based carbon samples were lower than that of the raw LFP based carbon samples. The carbon obtained was characterized using ultimate and proximate analyses. The surface morphological features and phase transformation of the synthesized micro-spherical carbon was characterized by a field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analysis. The results demonstrated that the extraction of lignin could significantly alter the end properties of the synthesized carbon sample. The carbon spheres derived from LFP showed a higher carbon content than the HC-based carbon. The absence of lignin in the holo-cellulose (HC) made it easy to disintegrate in comparison to the raw, LFP-based carbon samples during the HTC process. The carbonaceous samples (LFP-300 and HC-300) prepared at 300 °C were selected and their adsorption performance for Pb (II) cations was observed using Langmuir, Freundlich, and Temkin linear isotherm models. At 30 °C, the equilibrium data followed the Langmuir isotherm model more than the Freundlich and Temkin model for both the LFP-300 sample and the HC-300 sample. The potential of the synthesized carbon microspheres were further analyzed by thermodynamic characterizations of the adsorption equilibrium system.

Biochar modification to enhance sorption of inorganics from water

Biochar can be used as a sorbent to remove inorganic pollutants from water but the efficiency of sorption can be improved by activation or modification. This review evaluates various methods to increase the sorption efficiency of biochar including activation with steam, acids and bases and the production of biochar-based composites with metal oxides, carbonaceous materials, clays, organic compounds, and biofilms. We describe the approaches, and explain how each modification alters the sorption capacity. Physical and chemical activation enhances the surface area or functionality of biochar, whereas modification to produce biochar-based composites uses the biochar as a scaffold to embed new materials to create surfaces with novel surface properties upon which inorganic pollutants can sorb. Many of these approaches enhance the retention of a wide range of inorganic pollutants in waters, but here we provide a comparative assessment for Cd²⁺, Cu²⁺, Hg²⁺, Pb²⁺, Zn²⁺, NH₄⁺, NO₃^-, PO₄^3-, CrO₄^2- and AsO₄^3-.

Alkali modified hydrochar of grape pomace as a perspective adsorbent of Pb(2+) from aqueous solution

Hydrochar produced via hydrothermal carbonization of grape pomace was considered as novel sorbent of Pb(2+) from aqueous solution. In order to enhance the adsorption capacity, hydrochar was chemically modified using 2 M KOH solution. Both materials were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction technique. Batch experiments were performed to examine the effect of sorbent dosage, pH and contact time. Obtained results showed that the KOH treatment increased the sorption capacity of hydrochar from 27.8 mg g(-1) up to 137 mg g(-1) at pH 5. Adsorption of lead on either of the materials was achieved through ion-exchange mechanism, chemisorption and Pb(2+)-π interaction. The Sips isotherm model gave the best fit with the experimental data obtained for Pb(2+) sorption using activated hydrochar. The adsorption kinetic followed a pseudo second-order model. Thermodynamic parameters implied that the Pb(2+) binding for hydrochar surface was spontaneous and exothermic process. Findings from this work suggest that the hydrothermal carbonization is a promising route for production of efficient Pb (2+) sorbents for wastewater treatment.

Progress in the preparation and application of modified biochar for improved contaminant removal from water and wastewater

Modified biochar (BC) is reviewed in its preparation, functionality, applications and regeneration. The nature of precursor materials, preparatory conditions and modification methods are key factors influencing BC properties. Steam activation is unsuitable for improving BC surface functionality compared with chemical modifications. Alkali-treated BC possesses the highest surface functionality. Both alkali modified BC and nanomaterial impregnated BC composites are highly favorable for enhancing the adsorption of different contaminants from wastewater. Acidic treatment provides more oxygenated functional groups on BC surfaces. The Langmuir isotherm model provides the best fit for sorption equilibria of heavy metals and anionic contaminants, while the Freundlich isotherm model is the best fit for emerging contaminants. The pseudo 2(nd) order is the most appropriate model of sorption kinetics for all contaminants. Future research should focus on industry-scale applications and hybrid systems for contaminant removal due to scarcity of data.

Kinetics, thermodynamics and mechanistic studies of carbofuran removal using biochars from tea waste and rice husks

This study reports the thermodynamic application and non-linear kinetic models in order to postulate the mechanisms and compare the carbofuran adsorption behavior onto rice husk and tea waste derived biochars. Locally available rice husk and infused tea waste biochars were produced at 700 °C. Biochars were characterized by using proximate, ultimate and surface characterization methods. Batch experiments were conducted at 25, 35, and 45 °C for a series of carbofuran solutions ranging from 5 to 100 mg L(-1) with a biochar dose of 1 g L(-1) at pH 5.0 with acetate buffer. Molar O/C ratios indicated that rice husk biochar (RHBC700) is more hydrophilic than tea waste biochar (TWBC700). Negative ΔG (Gibbs free energy change) values indicated the feasibility of carbofuran adsorption on biochar. Increasing ΔG values with the rise in temperature indicated high favorability at higher temperatures for both RHBC and TWBC. Enthalpy values suggested the involvement of physisorption type interactions. Kinetic data modeling exhibited contribution of both physisorption, via pore diffusion, π*-π electron donor-acceptor interaction, H-bonding, and van der Waals dispersion forces and chemisorption via chemical bonding with phenolic, and amine groups. Equilibrium adsorption capacities of RHBC and TWBC determined by pseudo second order kinetic model were 25.2 and 10.2 mg g(-1), respectively.

Removal of levofloxacin from aqueous solution using rice-husk and wood-chip biochars

The potential for rice husk (RH) and wood chip (WC) biochars to remove levofloxacin (LEV) from aqueous solution was evaluated. The physical and chemical properties of the biochars were characterized using various tools and techniques. Furthermore, batch sorption experiments were conducted to determine the sorption ability of the biochars to LEV. The pseudo-second order kinetic model described the sorption kinetic data better than the pseudo-first order kinetic model and the Elovich equation because the process involved both surface adsorption and pore diffusion. For the isotherms, the Langmuir equation fitted the data better than the Freundlich equation. The maximum Langmuir sorption capacities of the biochars to LEV ranged from 1.49 to 7.72 mg g(-1). Thermodynamic parameters obtained from the experiments showed that the adsorption of LEV onto the WC biochar was spontaneous and exothermic, while its adsorption onto the RH biochar was spontaneous and endothermic under tested conditions. A mixture of 0.025 M phosphate buffer (80%, pH 3.0) and acetonitrile (20%) effectively desorbed the LEV from the biochars with a recovery rate up to 80%. Findings from this work indicate that biochars can be used as an alternative adsorbent to effectively remove emerging contaminants including LEV from aqueous solutions.

Engineered/designer biochar for contaminant removal/immobilization from soil and water: Potential and implication of biochar modification

The use of biochar has been suggested as a means of remediating contaminated soil and water. The practical applications of conventional biochar for contaminant immobilization and removal however need further improvements. Hence, recent attention has focused on modification of biochar with novel structures and surface properties in order to improve its remediation efficacy and environmental benefits. Engineered/designer biochars are commonly used terms to indicate application-oriented, outcome-based biochar modification or synthesis. In recent years, biochar modifications involving various methods such as, acid treatment, base treatment, amination, surfactant modification, impregnation of mineral sorbents, steam activation and magnetic modification have been widely studied. This review summarizes and evaluates biochar modification methods, corresponding mechanisms, and their benefits for contaminant management in soil and water. Applicability and performance of modification methods depend on the type of contaminants (i.e., inorganic/organic, anionic/cationic, hydrophilic/hydrophobic, polar/non-polar), environmental conditions, remediation goals, and land use purpose. In general, modification to produce engineered/designer biochar is likely to enhance the sorption capacity of biochar and its potential applications for environmental remediation.

Catalytic activation and application of micro-spherical carbon derived from hydrothermal carbonization of lignocellulosic biomass: statistical analysis using Box–Behnken design

Activated carbon was produced by physico-chemical activation of hydrothermally carbonized dried stem derived fromCorchorus olitorius, commonly known as Jute (JS), using potassium hydroxide (KOH) as an activation agent.