Application of biochar for the removal of pollutants from aqueous solutions

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-.

Low-Cost Carbon Fillers to Improve Mechanical Properties and Conductivity of Epoxy Composites

In recent years, low-cost carbons derived from recycled materials have been gaining attention for their potentials as filler in composites and in other applications. The electrical and mechanical properties of polymer composites can be tuned using different percentages and different kind of fillers: either low-cost (e.g., carbon black), ecofriendly (e.g., biochar), or sophisticated (e.g., carbon nanotubes). In this work, the mechanical and electrical behavior of composites with biochar and multiwall carbon nanotubes dispersed in epoxy resin are compared. Superior mechanical properties (ultimate tensile strength, strain at break) were noticed at low heat-treated biochar (concentrations 2⁻4 wt %). Furthermore, dielectric properties in the microwave range comparable to low carbon nanotubes loadings can be achieved by employing larger but manageable amounts of biochar (20 wt %), rending the production of composites for structural and functional application cost-effective.

Biochar based remediation of water and soil contaminated by phenanthrene and pentachlorophenol

Phenanthrene (Phe) and pentachlorophenol (PCP) are classified as persistent organic pollutants and represent serious concern for the environment as they are toxic and ubiquitous. Biochar based remediation is an emerging technology used in water and soil contamination. In this study we used poplar (BP) and conifer (BC) biochars to remediate water and soil contaminated by Phe and PCP. BP and BC were able to remove completely either Phe or PCP from contaminated water within one to three days. When biochar was confined in a porous membrane, BC and BP maintained their sorption efficiency for several remediation cycles. However, in these conditions BC allowed faster Phe removal. In soil remediation experiments, addition of two biochar rates, i.e. 2.5 and 5 mg g^-1, strongly reduced Phe extractability (up to 2.7% of the initially added Phe with the larger BC dose). This was similar to the behavior observed when compost was applied in order to verify the role of soil organic matter in the fate of both contaminants. PCP extractability was reduced only up to 75% (in average) in all samples including those with compost amendment. Only larger amount of biochar (20 and 50 mg g^-1) allowed reduction of the extractable PCP and nullified phytotoxicity of the contaminant.

Sorptive removal of ionizable antibiotic sulfamethazine from aqueous solution by graphene oxide-coated biochar nanocomposites: Influencing factors and mechanism

Significant concerns have been raised over antibiotics pollution in aquatic environments in recent years. In this study, sorption of sulfamethazine (SMT) by novel graphene oxide-coated biochar nanocomposites (GO-BC) based on graphene oxide (GO) with bamboo sawdust biochar (BC) was investigated. In comparison with the original BC, the sorption capacity of GO-BC for SMT increased by 1.14 times. Sorption of SMT onto GO-BC was proved to be dominantly by chemisorption, and Freundlich isotherm described the sorption adequately. It was found that variation of pH and ionic strength obviously affected the sorption of SMT, and GO-BC had a good sorption effect on SMT at pH 3.0-6.0 and lower ionic strength. Obvious enhancement (by 30%) in sorption of SMT on GO-BC was observed, which might be attributed to the increase of functional groups on the surface of GO-BC. Moreover, the main sorption mechanism for SMT was π-π electron-donor-acceptor interaction, while auxiliary sorption mechanisms were inferred as pore-filling, cation exchange, hydrogen bonding interaction and electrostatic interaction. The results indicated that GO-BC sorption was an efficient way for the removal of SMT.

Development of a novel biochar/PSF mixed matrix membrane and study of key parameters in treatment of copper and lead contaminated water

Mixed matrix membrane (MMM) has attracted increasing attentions in various applications, such as water treatment. In this study, an innovative biochar/polysulfone (PSF) mixed matrix hollow fiber membrane was fabricated by incorporating micro-sized biochar particles in the PSF matrix. It was demonstrated that the membrane was more hydrophilic than the pure PSF membrane. Higher water flux was obtained. The adsorption of copper and lead on the MMM increased as the pH was increased with the maximum adsorption capacity observed at pH > 4.5. The adsorption equilibrium was established in 7 and 12 h for lead and copper, respectively. The adsorption kinetics and isotherm followed the intraparticle surface diffusion model and Freundlich isotherm, respectively. The presence of humic acid (HA) had a little effect on the adsorption, while the ionic strength showed an adverse effect on the removal. In addition, the feed concentration and cross flow rate significantly affected the removal efficiency in a continuous filtration mode. The increase in feed concentration and cross flow rate resulted in a reduction in the volume of treated permeate that had the copper/lead concentrations below the regulated levels for drinking water. The MMM exhibited an excellent regeneration-reuse performance in the removal of both copper and lead. Finally, our mechanism studies indicated that the uptake of heavy metals was controlled by a combination of key reactions of complexation, ion-exchange and precipitation. This study indicated that the MMM can be applied as an effective and eco-friendly material for the treatment of heavy metals contaminated water.

Adsorption Removal of 17β-Estradiol from Water by Rice Straw-Derived Biochar with Special Attention to Pyrolysis Temperature and Background Chemistry

Rice straw biochar that produced at three pyrolysis temperatures (400, 500 and 600 °C) were used to investigate the adsorption properties of 17β-estradiol (E2). The biochar samples were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), elemental analysis and BET surface area measurements. The influences of pyrolysis temperature, E2 concentration, pH, ionic strength, background electrolyte and humic acid were studied. Kinetic and isotherm results illustrated that the adsorption process could be well described by pseudo-second-order and Freundlich models. Experimental results showed that ionic strength had less influence on the adsorption of E2 by 500 and 600 °C rice straw biochar. Further, multivalent ions had positive impact on E2 removal than monovalent ions and the influence of the pyrolysis temperature was unremarkable when background electrolyte existed in solutions. The adsorption capacity of E2 decreased with the pH ranged from 3.0 to 12.0 and the humic acid concentration from 2 to 10 mg L-1. Electrostatic attractions and π-π interaction were involved in the adsorption mechanisms. Compared to low-temperature biochar, high-temperature biochar exhibited a better adsorption capacity for E2 in aqueous solution, indicated it had a greater potential for E2 pollution control.

Enhanced adsorption of Cu(II) and Cd(II) by phosphoric acid-modified biochars

In this research, adsorption of Cu(II) and Cd(II) by biochars was investigated. To enhance the adsorption of these two metal ions, a simple modification of biochars by phosphoric acid (H₃PO₄) was carried out. The surface area was larger and the contents of oxygen-containing functional groups of modified biochars were more than pristine biochars. In comparison with pristine biochar, modified biochars sorbed Cu(II) and Cd(II) much more strongly. Surface area had significant effects on the sorption of Cu(II) and Cd(II) by modified biochars, it also resulted in the higher sorption for the pristine biochar at high pyrolysis temperature. X-ray photoelectron spectroscopy analyses indicated that the quantities of carboxyl (-COOH) and hydroxyl (-OH) functional groups of modified biochars were larger than those of pristine biochar at the same pyrolysis temperature. Compared with that of pristine biochars, the strong ability of -COOH and -OH of modified biochars to form complexes with Cu(II)/Cd(II) ions resulted in higher adsorption of these two metal ions. The phosphorus-containing groups of modified biochars, such as P=O and P=OOH from the result of Fourier transform infrared spectroscopy, interacted and also formed complexes with metal ions, possibly resulting in the enhanced adsorption of Cu(II) and Cd(II). Thus, sorption of metal ions by modified biochars was controlled by the mechanism of surface complexation between oxygen containing functional groups and metals. In general, the H₃PO₄ modification was an effective method to prepare biochars with a high affinity for the sorption of heavy metals.

Enhanced adsorption of hexavalent chromium by a biochar derived from ramie biomass (Boehmeria nivea (L.) Gaud.) modified with β-cyclodextrin/poly(L-glutamic acid)

This paper explored biochar modification to enhance biochar's ability to adsorb hexavalent chromium from aqueous solution. The ramie stem biomass was pyrolyzed and then treated by β-cyclodextrin/poly(L-glutamic acid) which contained plentiful functional groups. The pristine and modified biochar were characterized by FTIR, X-ray photoelectron spectroscopy, specific surface area, and zeta potential measurement. Results indicated that the β-cyclodextrin/poly(L-glutamic acid) was successfully bound to the biochar surface. Batch experiments were conducted to investigate the kinetics, isotherm, thermodynamics, and adsorption/desorption of Cr(VI). Adsorption capacities of CGA-biochar were significantly higher than that of the untreated biochar, and its maximum adsorption capacity could reach up to 197.21 mg/g at pH 2.0. Results also illustrated that sorption performance depended on initial solution pH; in addition, acidic condition was beneficial to the Cr(VI) uptake. Furthermore, the Cr(VI) uptake was significantly affected by the ion strength and cation species. This study demonstrated that CGA-biochar could be a potential adsorbent for Cr(VI) pollution control.

Phosphate recovery from liquid fraction of anaerobic digestate using four slow pyrolyzed biochars: Dynamics of adsorption, desorption and regeneration

Four slow pyrolyzed biochars produced from wood (WDB), corncobs (CCB), rice husks (RHB) and sawdust (SDB) were evaluated for adsorption, desorption and regeneration of phosphate (PO₄^3--P) from anaerobically digested liquid swine manure. The PO₄^3--P adsorption capacity increased followed by initial concentrations increasing. Maximum PO₄^3--P adsorptions at initial 150 mg/L of PO₄^3--P (highest load) were average of 7.67, 6.43, 5.73 and 5.41 mg/g for WDB, CCB, RHB and SDB, respectively. Pseudo second order kinetics model could best fit PO₄^3--P adsorption, which indicated the chemisorption via precipitation was the main mechanism for PO₄^3--P removal. The sorption process was reversible and the adsorbed PO₄^3--P could be desorbed in both neutral (57-78%) and acidic solution environments (75-88%) for all biochars. Meanwhile, regenerated biochar could re-adsorb up to 5.62 mg/g at the highest initial PO₄^3--P of 150 mg/L. The present finding implied biochar could be effectively used to recover PO₄^3--P from anaerobic digestate.

Treatment of refractory contaminants by sludge-derived biochar/persulfate system via both adsorption and advanced oxidation process

A novel strategy for the removal of refractory organic contaminants was realized through sludge-derived biochar (SDBC)/persulfate (PS) system via both adsorption and advanced oxidation process under ambient conditions. SDBC was prepared by one single step of slow pyrolysis of municipal sewage sludge, appeared a porous structure, and contained abundant oxygen-containing functional groups as well as amorphous Fe species. Large surface area and porous structure of SDBC benefitted the adsorption and enrichment of contaminants, while oxygen-containing functional groups and Fe species on the surface were considered as reactive components for the activation of PS. Under conditions of [PS]₀ = 1.85 mM, [4-chlorophenol]₀ = 0.039 mM, [SDBC]₀ = 1 g L^-1, pH₀ = 6.30 and temperature = 25 °C, the removal of model compound of 4-chlorophenol achieved 92.3%, and this significant performance of SDBC/PS system was consistent in a broad pH window. Radical scavengers and electron paramagnetic resonance (EPR) studies suggested that SDBC successfully activated PS to produce various oxidative radicals. Meanwhile, recycle experiments and Fe³⁺ leaching tests further demonstrated the stability of SDBC during the activation of PS. Municipal landfill leachate effluent through a membrane bio-reactor was testified as the refractory real wastewater, in which both the removal of total organic carbon and ammonia was significant. Thus, SDBC showed certain advantages in PS activation such as feasible preparation method, remarkable efficiency and stability. These advantages proved SDBC/PS system as an effective strategy of controlling waste by waste, and implicated its potential application in full-scale for the treatment of refractory organic contaminants.

Bio-butanol sorption performance on novel porous-carbon adsorbents from corncob prepared via hydrothermal carbonization and post-pyrolysis method

A series of porous-carbon adsorbents termed as HDPC (hydrochar-derived pyrolysis char) were prepared from corncob and used for the 1-butanol recovery from aqueous solution. The influences of pyrolysis temperature on properties of the adsorbents were systematically investigated. The results showed that hydrophobicity, surface area, and pore volume of HDPC samples increased with an increase in pyrolysis temperature. Furthermore, the adsorption mechanism of 1-butanol on the adsorbents was explored based on correlation of the samples properties with adsorption parameters extracted from the 1-butanol adsorption isotherms (K_F and Q_e12). Overall, the 1-butanol adsorption capacity increased with a decrease in polarity and an increase in aromaticity, surface area and pore volume of HDPC samples. However, at different pyrolysis temperature, the factors causing the increase of 1-butanol adsorption on the adsorbents are variable. The kinetic experiments revealed that the pores played a vital role in the 1-butonal adsorption process. The intraparticle diffusion model was used to predict the adsorption kinetic process. The simulation results showed that intraparticle diffusion was the main rate-controlling step in the 1-butanol adsorption process.

Characterization and Pb(II) removal potential of corn straw- and municipal sludge-derived biochars

Corn straw- and municipal sludge-derived biochars (CS-BC and MS-BC, respectively) were used to remove Pb(II) from aqueous solutions. Despite being pyrolysed at the same temperature (723 K), MS-BC showed higher porosity and hydrophobicity than CS-BC. The optimum biochar loading and pH values allowing efficient Pb(II) removal (greater than 80%) were 0.2 g l^-1 and 7.0, respectively. The presence of PO₄^3- (greater than 0.01 mol l^-1) significantly affected the adsorptive performance of Pb(II) on the biochar samples. The adsorption data fitted well to a pseudo-second-order kinetic model and a Langmuir model, and the maximum Pb(II) adsorption capacities were 352 and 387 mg g^-1 for CS-BC and MS-BC, respectively. The main mechanisms involved in the adsorption of Pb(II) on biochar were electrostatic attraction and surface complexation. When comparing both biochars, CS-BC showed better cost-effectiveness for the removal of Pb(II) from aqueous solutions.

A Valuable Biochar from Poplar Catkins with High Adsorption Capacity for Both Organic Pollutants and Inorganic Heavy Metal Ions

In this paper, biochar derived from poplar catkins was used as an economical and renewable adsorbent for adsorption organic and inorganic pollutants such as, dyes, organic compounds, and heavy metal ions from wastewater. Mesoporous activated carbonized poplar catkins (ACPCs) were produced from char as a by-product by carbonized poplar catkins (CPCs). With their high surface area, ACPCs exhibited the maximum adsorption capacities of 71.85 and 110.17 mg/g for the removal of inorganic U(VI) and Co(II). Compared other biochars adsorbents, ACPCs can also adsorb organic pollutants with the maximum adsorption capacities of 534, 154, 350, 148 and 384 mg/g for methylene blue (MB), methyl orange (MO), Congo red (CR), chloramphenicol (CAP) and naphthalene. The adsorption of organic pollutants was fitted with pseudo-first order, pseudo-second order, and intra-particle diffusion kinetic models figure out the kinetic parameters and adsorption mechanisms. Langmuir adsorption isotherm was found to be suitable for Co(II) and U(VI) adsorption and thermodynamic studies indicated adsorption processes to be endothermic and spontaneous. The adsorption process includes both outer-sphere surface complexes and hydrogen-bonding interactions. The results showed that biochar derived from poplar catkins was a potential material to remove pollutants in wastewater.

Effect of Temperature on the Structural and Physicochemical Properties of Biochar with Apple Tree Branches as Feedstock Material

The objective of this study was to study the structure and physicochemical properties of biochar derived from apple tree branches (ATBs), whose valorization is crucial for the sustainable development of the apple industry. ATBs were collected from apple orchards located on the Weibei upland of the Loess Plateau and pyrolyzed at 300, 400, 500 and 600 °C (BC300, BC400, BC500 and BC600), respectively. Different analytical techniques were used for the characterization of the different biochars. In particular, proximate and element analyses were performed. Furthermore, the morphological, and textural properties were investigated using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, Boehm titration and nitrogen manometry. In addition, the thermal stability of biochars was also studied by thermogravimetric analysis. The results indicated that the increasing temperature increased the content of fixed carbon (C), the C content and inorganic minerals (K, P, Fe, Zn, Ca, Mg), while the yield, the content of volatile matter (VM), O and H, cation exchange capacity, and the ratios of O/C and H/C decreased. Comparison between the different samples show that highest pH and ash content were observed in BC500. The number of acidic functional groups decreased as a function of pyrolysis temperature, especially for the carboxylic functional groups. In contrast, a reverse trend was found for the basic functional groups. At a higher temperature, the brunauer–emmett–teller (BET) surface area and pore volume are higher mostly due to the increase of the micropore surface area and micropore volume. In addition, the thermal stability of biochars also increased with the increasing temperature. Hence, pyrolysis temperature has a strong effect on biochar properties, and therefore biochars can be produced by changing pyrolysis temperature in order to better meet their applications.

Facile synthesis of Cu(II) impregnated biochar with enhanced adsorption activity for the removal of doxycycline hydrochloride from water

In this study, the effect factors and mechanisms of doxycycline hydrochloride (DOX) adsorption on copper nitrate modified biochar (Cu-BC) was investigated. Cu-BC absorbent was synthesized through calcination of peanut shells biomass at 450°C and then impregnation with copper nitrate. The Cu-BC has exhibited excellent sorption efficiency about 93.22% of doxycycline hydrochloride from aqueous solution, which was double higher than that of the unmodified biochar. The experimental results suggest that the adsorption efficiency of DOX on the Cu-BC is dominated by the strong complexation, electrostatic interactions between DOX molecules and the Cu-BC samples. Comprehensively considering the cost, efficiency and the application to realistic water, the Cu-BC hold the significant potential for enhancing the effectiveness to remove DOX from water.

Sorption of tetracycline on biochar derived from rice straw under different temperatures

Biochars produced from the pyrolysis of waste biomass under limited oxygen conditions could serve as adsorbents in environmental remediation processes. Biochar samples derived from rice straw that were pyrolyzed at 300 (R300), 500 (R500) and 700°C (R700) were used as adsorbents to remove tetracycline from an aqueous solution. Both the Langmuir and Freundlich models fitted the adsorption data well (R² > 0.919). The adsorption capacity increased with pyrolysis temperature. The R500 and R700 samples exhibited relative high removal efficiencies across a range of initial tetracycline concentrations (0.5mg/L-32mg/L) with the maximum (92.8%–96.7%) found for adsorption on R700 at 35°C. The relatively high surface area of the R700 sample and π–π electron-donor acceptor contributed to the high adsorption capacities. A thermodynamic analysis indicated that the tetracycline adsorption process was spontaneous and endothermic. The pH of solution was also found to influence the adsorption processes; the maximum adsorption capacity occurred at a pH of 5.5. These experimental results highlight that biochar derived from rice straw is a promising candidate for low-cost removal of tetracycline from water.

Adsorptive removal of ascertained and suspected endocrine disruptors from aqueous solution using plant-derived materials

The present study deals with the use of low-cost plant-derived materials, namely a biochar, spent coffee grounds, spent tea leaves, and a compost humic acid, for the adsorptive removal from water of two estrogens, 4-tert-octylphenol (OP) and 17-β-estradiol (E2), and two pesticides, carbaryl and fenuron, each spiked at a concentration of 1 mg L^-1. Kinetics and adsorption isotherms have been performed using a batch equilibrium method to measure the sorption capacities of the adsorbents towards the four molecules. Adsorption constants were calculated using the linear, Freundlich, and Langmuir models. Kinetics data obtained evidenced a rapid adsorption of each compound onto both biochar and coffee grounds with the attainment of a steady-state equilibrium in less than 4 h. Significant differences among the adsorbents and the compounds were found regarding the model and the extent of adsorption. In general, the estrogens were adsorbed more quickly and in greater amounts than the less hydrophobic pesticides, following the order: OP > E2 > carbaryl > fenuron. The ranges of Freundlich constants obtained for OP, E2, carbaryl, and fenuron onto the sorbents were 5049-2253, 3385-206, 2491-79, and 822-24 L kg^-1, respectively. The maximum values of constants were obtained for biochar, except for OP that was more adsorbed by spent coffee grounds. Adsorption kinetic data followed a pseudo-second-order model, thus indicating the occurrence of chemical interactions between the compounds and the substrates. The remarkable sorption capacities of all adsorbents towards the four molecules suggest the valuable exploitation of these materials for decontamination purposes, such as the treatment of wastewater before a feasible recycle in soil.

Adsorptive removal of Ni2+ and Cd2+ from wastewater using a green longan hull adsorbent

The adsorptive removal of Ni2+ and Cd2+ at concentrations of approximately 50 mg L−1 in wastewater is investigated using an agricultural adsorbent, longan hull, and the adsorptive mechanism is characterized. The maximum adsorption capacity of approximately 4.19 mg g−1 Cd2+ was obtained under the optimized conditions of room temperature, pH 5.0, and a solid-to-liquid ratio of 1:30 in approximately 15 min. For Ni2+, the maximum adsorption capacity of approximately 3.96 mg g−1 was obtained at pH 4.7 in approximately 20 min. The adsorption kinetics for both metal ions on the longan hull can be described by a pseudo second-order rate model and are well fitted to the Langmuir adsorption isotherm. The adsorption mechanism of the longan hull to Ni2+ and Cd2+ ions is shown to be a monolayer adsorption of metal ions onto the absorbent surface. Thereinto, the longan hull adsorbent contains N–H, C–H, C=O, and C=C functional groups that can form ligands when loaded with Ni2+ and Cd2+, which reduces the fluorescence of the dried longan hull material.

Biochar-based water treatment systems as a potential low-cost and sustainable technology for clean water provision

Approximately 600 million people lack access to safe drinking water, hence achieving Sustainable Development Goal 6 (Ensure availability and sustainable management of water and sanitation for all by 2030) calls for rapid translation of recent research into practical and frugal solutions within the remaining 13 years. Biochars, with excellent capacity to remove several contaminants from aqueous solutions, constitute an untapped technology for drinking water treatment. Biochar water treatment has several potential merits compared to existing low-cost methods (i.e., sand filtration, boiling, solar disinfection, chlorination): (1) biochar is a low-cost and renewable adsorbent made using readily available biomaterials and skills, making it appropriate for low-income communities; (2) existing methods predominantly remove pathogens, but biochars remove chemical, biological and physical contaminants; (3) biochars maintain organoleptic properties of water, while existing methods generate carcinogenic by-products (e.g., chlorination) and/or increase concentrations of chemical contaminants (e.g., boiling). Biochars have co-benefits including provision of clean energy for household heating and cooking, and soil application of spent biochar improves soil quality and crop yields. Integrating biochar into the water and sanitation system transforms linear material flows into looped material cycles, consistent with terra preta sanitation. Lack of design information on biochar water treatment, and environmental and public health risks constrain the biochar technology. Seven hypotheses for future research are highlighted under three themes: (1) design and optimization of biochar water treatment; (2) ecotoxicology and human health risks associated with contaminant transfer along the biochar-soil-food-human pathway, and (3) life cycle analyses of carbon and energy footprints of biochar water treatment systems.

Pyrolysis wastewater treatment by adsorption on biochars produced by poplar biomass

Pyrolysis is a widely studied thermochemical process, however the disposal of the produced byproducts is an unexplored field. In particular, the acqueous phase, characterized by a high organic load (TOC), must be necessarily treated. Aims of this work is to study the potentiality of biochar as adsorbent material for the treatment of this wastewater. For this aim, pyrolysis wastewater and biochar produced in the same plant were used. Two biochars produced at different temperatures (550 and 750 °C) and an activated biochar produced by chemical activation with NaOH of the raw biomass were tested. The study shows that higher temperature in the biochar production leads to higher sorption capacity of the organic compounds due to an increase of the surface area. The activation process further increases the surface area of the biochar that becomes similar to that of a commercial activated carbon while the sorption capacity exceeds that of commercial activated carbon of 2.5 times.

Mechanisms of metal sorption by biochars: Biochar characteristics and modifications

Biochar produced by thermal decomposition of biomass under oxygen-limited conditions has received increasing attention as a cost-effective sorbent to treat metal-contaminated waters. However, there is a lack of information on the roles of different sorption mechanisms for different metals and recent development of biochar modification to enhance metal sorption capacity, which is critical for biochar field application. This review summarizes the characteristics of biochar (e.g., surface area, porosity, pH, surface charge, functional groups, and mineral components) and main mechanisms governing sorption of As, Cr, Cd, Pb, and Hg by biochar. Biochar properties vary considerably with feedstock material and pyrolysis temperature, with high temperature producing biochars with higher surface area, porosity, pH, and mineral contents, but less functional groups. Different mechanisms dominate sorption of As (complexation and electrostatic interactions), Cr (electrostatic interactions, reduction, and complexation), Cd and Pb (complexation, cation exchange, and precipitation), and Hg (complexation and reduction). Besides sorption mechanisms, recent advance in modifying biochar by loading with minerals, reductants, organic functional groups, and nanoparticles, and activation with alkali solution to enhance metal sorption capacity is discussed. Future research needs for field application of biochar include competitive sorption mechanisms of co-existing metals, biochar reuse, and cost reduction of biochar production.

Removal of hexavalent chromium upon interaction with biochar under acidic conditions: mechanistic insights and application

Chromium pollution of soil and water is a serious environmental concern due to potential carcinogenicity of hexavalent chromium [Cr(VI)] when ingested. Eucalyptus bark biochar (EBB), a carbonaceous black porous material obtained by pyrolysis of biomass at 500 °C under oxygen-free atmosphere, was used to investigate the removal of aqueous Cr(VI) upon interaction with the EBB, the dominant Cr(VI) removal mechanism(s), and the applicability to treat Cr(VI)-contaminated wastewater. Batch experiments showed complete removal of aqueous Cr(VI) at pH 1-2; sorption was negligible at pH 1, but ~55% of total Cr was sorbed onto the EBB surface at pH 2. Detailed investigations on unreacted and reacted EBB through Fourier transform infrared spectroscopy and X-ray photoelectron spectrometry (XPS) indicate that the carboxylic groups in biochar played a dominant role in Cr(VI) sorption, whereas the phenolic groups were responsible for Cr(VI) reduction. The predominance of sorption-reduction mechanism was confirmed by XPS studies that indicated ~82% as Cr(III) and ~18% as Cr(VI) sorbed on the EBB surface. Significantly, Cr(VI) reduction was also facilitated by dissolved organic matter (DOM) extracted from biochar. This reduction was enhanced by the presence of biochar. Overall, the removal of Cr(VI) in the presence of biochar was affected by sorption due to electrostatic attraction, sorption-reduction mediated by surface organic complexes, and aqueous reduction by DOM. Relative dominance of the aqueous reduction mechanism depended on a critical biochar dosage for a given electrolyte pH and initial Cr(VI) concentration. The low-cost EBB developed here successfully removed all Cr(VI) in chrome tanning acidic wastewater and Cr(VI)-contaminated groundwater after pH adjustment, highlighting its potential applicability in effective Cr(VI) remediation.

Adsorption of emerging contaminant metformin using graphene oxide

The occurrence of emerging contaminants in our water resources poses potential threats to the livings. Due to the poor treatment in wastewater management, treatment technologies are needed to effectively remove these products for living organism safety. In this study, Graphene oxide (GO) was tested for the first time for its capacity to remove a kind of emerging wastewater contaminants, metformin. The research was conducted by using a series of systematic adsorption and kinetic experiments. The results indicated that GO could rapidly and efficiently reduce the concentration of metformin, which could provide a solution in handling this problem. The uptake of metformin on the graphene oxide was strongly dependent on temperature, pH, ionic strength, and background electrolyte. The adsorption kinetic experiments revealed that almost 80% removal of metformin was achieved within 20 min for all the doses studied, corresponding to the relatively high k₁ (0.232 min^-1) and k₂ (0.007 g mg^-1 min^-1) values in the kinetic models. It indicated that the highest adsorption capacity in the investigated range (q_m) of GO for metformin was at pH 6.0 and 288 K. Thermodynamic study indicated that the adsorption was a spontaneous (ΔG⁰ < 0) and exothermic (ΔH⁰ < 0) process. The adsorption of metformin increased when the pH values changed from 4.0 to 6.0, and decreased adsorption were observed at pH 6.0-11.0. GO still exhibited excellent adsorption capacity after several desorption/adsorption cycles. Besides, both so-called π-π interactions and hydrogen bonds might be mainly responsible for the adsorption of metformin onto GO.

Bio- and hydrochars from rice straw and pig manure: Inter-comparison

Conversion of rice straw (RS) and pig manure (PM) into chars is a promising disposal/recycling option. Herein, pyrolysis and hydrothermal carbonization were used to produce bio- and hydrochars from RS and PM, affording lower biochar (300-700°C) and hydrochar (180-300°C) yields at higher temperatures within the specified range. The C contents and C/N ratios of RS chars were higher than those of PM ones, with the opposite trend observed for yield and ash content. C and ash contents increased with increasing temperature, whereas H/C, O/C, and (O+N)/C ratios decreased. The lower H/C ratio of biochars compared to that of hydrochars indicated greater stability of the former. KCl was the main inorganic fraction in RS biochars, whereas quartz was dominant in PM biochars, and albite in PM hydrochars. Thus, RS is more suitable for carbon sequestration, while PM is more suitable for use as a soil amendment substrate.

Preparation of biochar by simultaneous carbonization, magnetization and activation for norfloxacin removal in water

Activated magnetic biochar (AMB) was prepared with corn stalks, reed stalks, and willow branches by simultaneous carbonization, magnetization, and activation, and used for norfloxacin removal in water. The exploration results showed that the zeta potential was positively charged at pH 2-10. These prepared activated magnetic biochars have a large specific surface area (>700m²·g^-1) and pore volume (>0.3cm³·g^-1). The quasi-second-order kinetic adsorption equation could better describe the adsorption of NOR on AMB. The Langmuir isotherm showed the better fitting results on AMB. The AMB showed the strong adsorption of NOR, and the saturated adsorption capacity of corn activated magnetic biochar was the highest, 7.6249mg·g^-1. The adsorption of NOR on AMB was a spontaneous endothermic process. The effect of pH on the adsorption behaviors of NOR on AMB was not obvious, and AMB had a good adsorption effect on NOR in a wide pH range.

Comparison of unusual carbon-based working electrodes for electrochemiluminescence sensors

In this work, unconventional carbon-based materials were investigated for use in electrochemiluminescence (ECL) working electrodes. Precursors such as bamboo, pistachio shells, kevlar^® fibers and camphor were differently treated and used as working electrodes in ECL experiments. After a proper process they were assembled as electrodes and tested in an electrochemical cell. Comparison among them and with a commercial glassy carbon electrode (GCE) shows a very good response for all of them thus demonstrating their potential use as disposable low-cost electrodes for early detection electrochemical analysis.

In-situ biogas upgrading during anaerobic digestion of food waste amended with walnut shell biochar at bench scale

A modified version of an in-situ CO₂ removal process was applied during anaerobic digestion of food waste with two types of walnut shell biochar at bench scale under batch operating mode. Compared with the coarse walnut shell biochar, the fine walnut shell biochar has a higher ash content (43 vs. 36 wt%) and higher concentrations of calcium (31 vs. 19 wt% of ash), magnesium (8.4 vs. 5.6 wt% of ash) and sodium (23.4 vs. 0.3 wt% of ash), but a lower potassium concentration (0.2 vs. 40% wt% of ash). The 0.96-3.83 g biochar (g VS_added)^-1 fine walnut shell biochar amended digesters produced biogas with 77.5%-98.1% CH₄ content by removing 40%-96% of the CO₂ compared with the control digesters at mesophilic and thermophilic temperature conditions. In a direct comparison at 1.83 g biochar (g VS_added)^-1, the fine walnut shell biochar amended digesters (85.7% CH₄ content and 61% CO₂ removal) outperformed the coarse walnut shell biochar amended digesters (78.9% CH₄ content and 51% CO₂ removal). Biochar addition also increased alkalinity as CaCO₃ from 2800 mg L^-1 in the control digesters to 4800-6800 mg L^-1, providing process stability for food waste anaerobic digestion.

Conversion of post consumer waste polystyrene into a high value adsorbent and its sorptive properties for Congo Red removal from aqueous solution

Using post-consumer waste polystyrene (WPS), a conjugated microporous polymer (CMP) was synthesised and activated into a sulphonic-group carrying resin (SCMP). The surface chemistry of the materials showed a decline in both the aromatic CH and aliphatic CH₂ stretching vibrations confirming successful crosslinking. The synthesised polymers were thermally stable with decomposition temperatures above 300 °C, had surface heterogeneity, and BET surface areas of 752 and 510 m²/g, respectively. A distribution of pores ranging from meso- to micro-pores was comparable to other CMPs. The materials had maximum adsorption capacities of 500 and 357 mg/g for Congo Red (CR) on CMP and SCMP, respectively. Converting waste polystyrene to an adsorbent is a cost effective way of handling waste and simultaneously providing material for wastewater remediation.

Biochars with excellent Pb(II) adsorption property produced from fresh and dehydrated banana peels via hydrothermal carbonization

Fresh and dehydrated banana peels were used as biomass feedstock to produce highly effective sorbent biochars through a facile one-step hydrothermal carbonization approach with 20%vol phosphoric acid as the reaction medium. The elemental ratio of oxygen content of the two as-prepared biochars were about 20%, and the FT-IR analysis confirmed the existence of abundant surface functional groups such as hydroxyl and carboxyl which greatly enhanced the adsorption performance. The sorbents showed excellent lead clarification capability of 359mg·g^-1 and 193mg·g^-1 for dehydrated and fresh banana peels based biochars, respectively. The change of the CO/OCO and the appearance of PbO/PbOC on the surface after adsorption confirmed that the ion exchange might be the dominant mechanism. The dehydration and pulverization pre-treatment and the addition of phosphoric acid can benefit the formation of those functional groups and hydrothermal carbonization can be a promising method to transfer biomass like fruit peels into biochars with excellent adsorption performance.

Immobilized laccase on oxygen functionalized nanobiochars through mineral acids treatment for removal of carbamazepine

Biocatalytic treatment with oxidoreductase enzymes, especially laccases are an environmentally benign method for biodegradation of pharmaceutical compounds, such as carbamazepine to less harmful compounds. However, enzymes are required to be immobilized on supports to be reusable and maintain their activity. Functionalization of support prior to immobilization of enzyme is highly important because of biomolecule-support interface on enzyme activity and stability. In this work, the effect of oxidation of nanobiochar, a carbonaceous material produced by biomass pyrolysis, using HCl, H₂SO₄, HNO₃ and their mixtures on immobilization of laccase has been studied. Scanning electron microscopy indicated that the structure of nanobiochars remained intact after oxidation and Fourier transform infrared spectroscopy confirmed the formation of carboxylic groups because of acid treatment. Titration measurements showed that the sample treated with H₂SO₄/HNO₃ (50:50, v/v) had the highest number of carboxylic groups (4.7mmol/g) and consequently the highest efficiency for laccase immobilization. Additionally, it was observed that the storage, pH and thermal stability of immobilized laccase on functionalized nanobiochar was improved compared to free laccase showing its potential for continuous applications. The reusability tests towards oxidation of 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) showed that the immobilized laccase preserved 70% of the initial activity after 3cycles. Finally, using immobilized laccase for degradation of carbamazepine exhibited 83% and 86% removal in spiked water and secondary effluent, respectively.

Biodegradation of the benzo[a]pyrene-contaminated sediment of the Jiaozhou Bay wetland using Pseudomonas sp. immobilization

To remove benzo[a]pyrene (BaP) that has accumulated in the Jiaozhou Bay wetland sediment, two strains (JB1 and JB2) were selected from the BaP-contaminated the wetland sediment and immobilized in coal cinder and chitosan beads using entrapping and surface adsorption methods. Biodegradation of BaP in sediment was carried out in pots. The results showed that, supported by the coal cinder and chitosan beads, 71.9, 65.5, 58.9 and 66.1% of the BaP in the immobilized cells was degraded after 40d. These percentages were clearly higher than the 47.7% that degraded from free cells. Kinetic analysis indicated that the immobilized gel-beads might remove BaP by multiple control steps. Compared to the chitosan, coal cinder-entrapping beads exhibited a higher removal rate for BaP; however, the degradation rates from coal cinder- and chitosan-surface adsorption beads were almost the same. This result indicates that in addition to the BaP-degrading bacteria, carrier materials and immobilizing methods play an important role in determining the success of a biodegradation strategy.

Metal immobilization by sludge-derived biochar: roles of mineral oxides and carbonized organic compartment

Pyrolyzing sludge into biochar is a potentially promising recycling/disposal solution for municipal wastewater sludge, and the sludge-derived biochar (SDBC) presents an excellent sorbent for metal immobilization. As SDBC is composed of both mineral oxides and carbonized organic compartment, this study therefore compared the sorption behaviour of Pb and Zn on SDBC to those of individual and mixture of activated carbon (AC) and amorphous aluminium oxide (Al₂O₃). Batch experiments were conducted at 25 and 45 °C, and the metal-loaded sorbents were artificially aged in the atmosphere for 1-60 days followed by additional sorption experiments. The Pb sorption was generally higher than Zn sorption, and the co-presence of Pb reduced Zn sorption on each studied sorbent. Higher sorption capacities were observed at 45 °C than 25 °C for SDBC and AC, while the opposite was shown for Al₂O₃, indicating the significance of temperature-dependent diffusion processes in SDBC and AC. Nevertheless, metal sorption was more selective on Al₂O₃ that showed a greater affinity towards Pb over Zn under competition, correlating with the reducible fraction of sequential extraction. Furthermore, significant amounts of Pb and Zn were additionally sorbed on SDBC following 30-day ageing. The X-ray diffraction revealed the formation of metal-phosphate precipitates, while the X-ray photoelectron spectroscopy showed a larger quantity of metal-oxygen bonding after 30-day ageing of metal-loaded SDBC. The results may imply favourable long-term transformation and additional sorption capacity of SDBC. In conclusion, SDBC resembles the sorption characteristics of both organic and mineral sorbents in different aspects, presenting an appropriate material for metal immobilization during soil amendment.

Removal of Zinc from Aqueous Solution by Optimized Oil Palm Empty Fruit Bunches Biochar as Low Cost Adsorbent

This study aims to produce optimized biochar from oil palm empty fruit bunches (OPEFB), as a green, low cost adsorbent for uptake of zinc from aqueous solution. The impact of pyrolysis conditions, namely, highest treatment temperature (HTT), heating rate (HR), and residence time (RT) on biochar yield and adsorption capacity towards zinc, was investigated. Mathematical modeling and optimization of independent variables were performed employing response surface methodology (RSM). HTT was found to be the most influential variable, followed by residence time and heating rate. Based on the central composite design (CCD), two quadratic models were developed to correlate three independent variables to responses. The optimum production condition for OPEFB biochar was found as follows: HTT of 615°C, HR of 8°C/min, and RT of 128 minutes. The optimum biochar showed 15.18 mg/g adsorption capacity for zinc and 25.49% of yield which was in agreement with the predicted values, satisfactory. Results of the characterization of optimum product illustrated well-developed BET surface area and porous structure in optimum product which favored its sorptive ability.

Pyrolysis for exploitation of biomasses selected for soil phytoremediation: Characterization of gaseous and solid products

Biomasses to be used in the phytoremediation process are generally selected to match agronomic parameters and heavy metals uptake ability. A proper selection can be made greatly effective if knowledge of the properties of the residual char from pyrolysis is available to identify possible valorization routes. In this study a comparative analysis of the yields and characteristics of char obtained from slow pyrolysis of five uncontaminated biomasses (Populus nigra, Salix alba, Fraxinus oxyphylla, Eucalyptus occidentalis and Arundo donax) was carried out under steam atmosphere to better develop char porosity. Moreover, the dependence of the properties of solid residue on the process final temperature was studied for E. occidentalis in the temperature range of 688-967K. The results demonstrate that, among the studied biomasses, chars from P. nigra and E. occidentalis have to be preferred for applications regulated by surface phenomena given their highest surface area (270-300m²/g), whereas char from E. occidentalis is the best choice when the goal is to maximize energy recovery.

Biochar as potential sustainable precursors for activated carbon production: Multiple applications in environmental protection and energy storage

There is a growing interest of the scientific community on production of activated carbon using biochar as potential sustainable precursors pyrolyzed from biomass wastes. Physical activation and chemical activation are the main methods applied in the activation process. These methods could have significantly beneficial effects on biochar chemical/physical properties, which make it suitable for multiple applications including water pollution treatment, CO₂ capture, and energy storage. The feedstock with different compositions, pyrolysis conditions and activation parameters of biochar have significant influences on the properties of resultant activated carbon. Compared with traditional activated carbon, activated biochar appears to be a new potential cost-effective and environmentally-friendly carbon materials with great application prospect in many fields. This review not only summarizes information from the current analysis of activated biochar and their multiple applications for further optimization and understanding, but also offers new directions for development of activated biochar.

The challenges of anaerobic digestion and the role of biochar in optimizing anaerobic digestion

Biochar, like most other adsorbents, is a carbonaceous material, which is formed from the combustion of plant materials, in low-zero oxygen conditions and results in a material, which has the capacity to sorb chemicals onto its surfaces. Currently, research is being carried out to investigate the relevance of biochar in improving the soil ecosystem, digestate quality and most recently the anaerobic digestion process. Anaerobic digestion (AD) of organic substrates provides both a sustainable source of energy and a digestate with the potential to enhance plant growth and soil health. In order to ensure that these benefits are realised, the anaerobic digestion system must be optimized for process stability and high nutrient retention capacity in the digestate produced. Substrate-induced inhibition is a major issue, which can disrupt the stable functioning of the AD system reducing microbial breakdown of the organic waste and formation of methane, which in turn reduces energy output. Likewise, the spreading of digestate on land can often result in nutrient loss, surface runoff and leaching. This review will examine substrate inhibition and their impact on anaerobic digestion, nutrient leaching and their environmental implications, the properties and functionality of biochar material in counteracting these challenges.

The role of ash content on bisphenol A sorption to biochars derived from different agricultural wastes

Inorganic minerals are important compositions in biochars, but their roles in biochar functions are investigated limitedly, which restricted our understanding on biochar applications. This study applied different biomasses to produce biochars. Their properties as well as sorption to bisphenol A (BPA) were studied, with a major focus on the role of inorganic compositions. Oxalates, carbonates, as well as KCl crystals were observed in the produced biochars depending on the feedstocks and temperatures. Oxalates and KCl formed at relatively low temperature (200-300 °C), while carbonates generally formed at pyrolysis temperature above 400 °C. The separated insoluble crystal particles and the dissolved salts have limited contribution to the apparent BPA sorption, but ash content removal altered BPA sorption. The potential impact of inorganic composition to BPA sorption should be resulted from biochar properties. Based on biochar characterization and sorption comparison before and after ash removal, we proposed that the formation of inorganic mineral compositions in biochar particles may have blocked the inner pores, which limited the significance of these sorption sites. As a result, the interactions of BPA and biochars were mostly determined by biochar surface functional groups. The acid treatment removed most of the inorganic compositions, and exposed more sorption sites, which consequently increased BPA sorption. Biochar sorption capacity may be further increased if the accessibility of the inner pores could be enhanced.

The systematic characterization of nanoscale bamboo charcoal and its sorption on phenanthrene:A comparison with microscale

This study investigated the characteristics of nanoscale bamboo charcoal (NBC), and made a comparison with microscale bamboo charcoal (MBC) on how they impact on the sorption abilities of different soils. The two charcoals contained similar elemental contents (e.g., high C, low H and low N) and various functional groups on their surfaces (e.g., aromatic structure, carboxyl, and hydroxyl). However, NBC had a larger total pore volume than that of MBC and was more likely to generate multi-layer sorption of phenanthrene. Controlled by van der Waals forces and electrostatic forces, NBC formed meso-and macropores (intra-particle porosity) and a more intricate pore structure. The performance of NBC in aqueous and soil-water systems was conspicuous and impressing. In aqueous system, by virtue of its larger pore volume, surface area and nonprotonated aromatic carbon, the K_d (sorption coefficient) of NBC reached up to 1.24×10⁶, almost 10 times higher than that of MBC. In soil-water systems, although it could aggregate and react with compounds in soil, the performance of NBC was not weakened by the complicated soil properties, and was still more capable of phenanthrene sorption than MBC, even at an extremely low addition rate 0.2% in soils. Additionally, in comparison with some other common biochars, NBC still showed a promising capacity for phenanthrene sorption in two systems. This finding increases our knowledge of NBC for the remediation of organic pollutants in soil and indicates that the addition rate of charcoals in soils could be reduced by lessening the particle size. Therefore, NBC provides a new possibility for soil pollutant remediation and deserves further research.

Biochar characteristics produced from rice husks and their sorption properties for the acetanilide herbicide metolachlor

Rice husk biochar (RHBC) was prepared for use as adsorbents for the herbicide metolachlor. The characteristics and sorption properties of metolachlor adsorbed by the RHBC prepared at different pyrolysis temperatures were determined by analysis of physico-chemical characteristics, Fourier transform infrared spectroscopy (FTIR), Boehm titration, scanning electron microscopy (SEM), and thermodynamics and kinetics adsorption. With increasing pyrolysis temperature, the RHBC surface area greatly increased (from 2.57 to 53.08 m² g^-1). RHBC produced at the highest temperature (750 °C) had the greatest surface area; SEM also showed the formation of a porous surface on RH-750 biochar. The sorption capacity of RHBC also increased significantly with increasing pyrolysis temperature and was characterized by the Freundlich constant K _f for the adsorption capacity increasing from 125.17-269.46 (pyrolysis at 300 °C) to 339.94-765.24 (pyrolysis at 750 °C). The results indicated that the surface area and pore diameter of RHBC produced with high pyrolysis temperature (i.e., 750 °C) had the greatest impact on the adsorption of metolachlor. The FTIR, Boehm titration, and SEM analysis showed that the greatest number of surface groups were on RHBC produced at the lowest temperature (300 °C). The biochars produced at different pyrolysis temperatures had different mechanisms of adsorbing metolachlor, which exhibited a transition from hydrogen bonds dominant at low pyrolytic temperature to pore-filling dominant at higher pyrolytic temperature.

Effects of the biochar aromaticity and molecular structures of the chlorinated organic compounds on the adsorption characteristics

Adsorption behaviors of the chlorinated organic compounds (COCs) (i.e., trichloroethylene (TCE), 1,2,4-trichlorobenzene (1,2,4-TCB); 1,2-dichlorobenzene (1,2-DCB); and monochlorobenzene (MCB)) by the commercial rice husk-based biochar (RH500) and the laboratory-prepared biochars from corn stalks under different pyrolytic temperatures (i.e., CS300, CS500, CS700) were examined and interpreted by the pseudo-first-order kinetic model, the double layer model with two energies, and the Freundlich model. It is identified that the first-order adsorption rate constants (k ₁ = 0.06∼0.51 h^-1) were proportional to the high aromaticity and/or low polarity of biochars and the strong hydrophobicity of the COCs. The saturated adsorption capacity for the COCs was followed by the order of RH500 > CS500 > CS700 > CS300. RH500 showed the highest adsorption capacity for the COCs due to its high surface area (SA) and total pore volume (TPV). However, CS500 with low SA and TPV development highlighted the important roles of the aromaticity and/or low polarity on the COCs adsorption. In addition, 1,2,4-TCB showed the highest saturated adsorption capacity on all biochars, followed by TCE, 1,2-DCB, and MCB. The results further revealed the positive effects of the physical properties (α, N _M, ε ₁, and ε ₂), the hydrophobicity and electrostatic forces (i.e., π-π interaction and electron donor-acceptor interaction) between the adsorbates and the aromatic moieties of biochar surfaces on the adsorption of COCs.

Effect of pyrolysis temperature on characteristics and aromatic contaminants adsorption behavior of magnetic biochar derived from pyrolysis oil distillation residue

The magnetic biochars were easily fabricated by thermal pyrolysis of Fe(NO₃)₃ and distillation residue derived from rice straw pyrolysis oil at 400, 600 and 800°C. The effects of pyrolysis temperature on characteristics of magnetic biochars as well as adsorption capacity for aromatic contaminants (i.e., anisole, phenol and guaiacol) were investigated carefully. The degree of carbonization of magnetic biochars become higher as pyrolysis temperature increasing. The magnetic biochar reached the largest surface area and pore volume at the pyrolysis temperature of 600°C due to pores blocking in biochar during pyrolysis at 800°C. Based on batch adsorption experiments, the used adsorbent could be magnetically separated and the adsorption capacity of anisole on magnetic biochars was stronger than that of phenol and guaiacol. The properties of magnetic biochar, including surface area, pore volume, aromaticity, grapheme-like-structure and iron oxide (γ-Fe₂O₃) particles, showed pronounced effects on the adsorption performance of aromatic contaminants.

Enhanced removal of Cd(ii) from aqueous solution using CaCO3 nanoparticle modified sewage sludge biochar

Nanostructured CaCO₃ modified sewage sludge biochar (CMSSB) was successfully fabricated for efficient removal of Cd(ii) from aqueous solutions.