The potential of biochar-photocatalytic nanocomposites for removal of organic micropollutants from wastewater

Pinecone biochar for the Adsorption of chromium (VI) from wastewater: Kinetics, thermodynamics, and adsorbent regeneration

High concentration of chromium in aquatic environments is the trigger for researchers to remediate it from wastewater environments. However, conventional water treatment methods have not been satisfactory in removing chromium from water and wastewater over the last decade. Similarly, many adsorption studies have been focused on one aspect of the treatment, but this study dealt with all aspects of adsorption packages to come up with a concrete conclusion. Therefore, this study aimed to prepare pinecone biochar (PBC) via pyrolysis and apply it for Cr(VI) removal from wastewater. The PBC was characterized using FTIR, SEM-EDX, BET surface area, pHpzc, Raman analyses, TGA, and XRD techniques. Chromium adsorption was studied under the influence of PBC dose, solution pH, initial Cr(VI) concentration, and contact time. The characteristics of PBC are illustrated by FTIR spectroscopic functional groups, XRD non-crystallite structure, SEM rough surface morphology, and high BET surface area125 m2/g, pore volume, 0.07 cm3/g, and pore size 1.4 nm. On the other hand, the maximum Cr (VI) adsorption of 69% was found at the experimental condition of pH 2, adsorbent dosage 0.25 mg/50 mL, initial Cr concentration 100 mg/L, and contact time of 120 min. Similarly, the experimental data were well-fitted with the Langmuir adsorption isotherm at R2 0.96 and the pseudo-second-order kinetics model at R2 0.99. This implies the adsorption process is mainly attributed to monolayer orientation between the adsorbent and adsorbate. In the thermodynamics study of adsorption, ΔG was found to be negative implying the adsorption process was feasible and spontaneous whereas the positive values of ΔH and ΔS indicated the adsorption process was endothermic and increasing the degree of randomness, respectively. Finally, adsorbent regeneration and reusability were successful up to three cycles. In conclusion, biochar surface modification and reusability improvements are urgently required before being applied at the pilot scale.

Removal of chromium(III) from contaminated waters using cobalt ferrite: how safe is remediated water to aquatic wildlife?

The release of hazardous elements by industrial effluents to aquatic ecosystems is a potential threat to the environment. Chromium (Cr) is one of the elements whose levels in several freshwater ecosystems should be reduced to promote water reuse. In recent years, magnetic materials have gained increasing interest as sorbents because of their easy removal from treated water through magnetic separation. In this study, colloidal cobalt ferrite (CoFe2O4) particles were investigated as magnetic sorbents for chromium-aqueous chemical species. The oxidative stress responses of Mytilus galloprovincialis mussels exposed to 200 μg/L of Cr, resembling remediated water, were evaluated. More than 95% of Cr was removed from contaminated solutions by CoFe2O4 aqueous suspensions at pH 6 and pH 10. The kinetics of sorption experiments were examined using pseudo-1st order, pseudo-2nd order and Elovich models to evaluate which mathematical model has a better adjustment to the experimental data. The present study revealed that the levels of Cr that remained in remediated water induced limited biochemical changes in mussels, being considered safe for aquatic systems. Overall, the use of cobalt ferrite-based sorbents may constitute a promising approach to remediate contaminated water.

A novel nano-cerium oxide functionalized biochar composite for degradation of organic dye: insight of the photocatalysis mechanism

Recently, visible-light-driven photocatalysis attracts much concerns in the remediation of environmental organic pollutants. In this study, the cerium doped biochar was fabricated through the hydrothermal method, and served as an efficient photocatalyst towards rhodamine B degradation under visible light irradiation. Almost 100% of rhodamine B was removed by 2.0 g·L-1 cerium doped biochar after 60 min of visible light irradiation at pH 3, but only about 25.50% and 29.60% of rhodamine B was removed by cerium dioxide and biochar under identical conditions. The degradation process coincided well with the pseudo-first-order kinetic model, and the photodegradation rate constant of cerium doped biochar was 0.0485·min-1, which was respectively 97 and 44 times that of biochar (0.0005·min-1) and cerium dioxide (0.0011·min-1). According to the trapping experiments and electron spin resonance spectroscopy analysis, h+, O2-∙ and ∙OH all participated in the degradation of rhodamine B in the cerium doped biochar photocatalytic systems, and the function of h+ and ∙OH was dominated. Consequently, the biochar could not only be an excellent carrier for supporting cerium dioxide, but also greatly improved its photocatalytic activity. The band gap of cerium doped biochar was narrower than cerium dioxide, which could improve the separation and migration of photogenerated electron-hole pairs under visible-light excitation, thus ultimately enhanced the degradation of rhodamine B. This work provided a deeper understanding of the preparation of biochar-based photocatalyst and its application in the remediation of environmental organic pollution.

Selective stepwise adsorption for enhanced removal of multi-component dissolved organic chemicals from petrochemical wastewater

The coexistence of multi-component dissolved organic chemicals causes tremendous challenge in purifying petrochemical wastewater, and stepwise selective adsorption holds the most promise for enhanced treatments. This study is designed to enhance the removal of multiple dissolved organic chemicals by stepwise adsorption. Special attention is given to the selective removal mechanisms for the major pollutant N,N-dimethylformamide (DMF), the sensitive pollutant fluorescent dissolved organic matter (FDOM) and other components. The results indicated that the combination of coal activated carbon and aluminum silica gel produced a synergistic effect and broke the limitation of removing only certain pollutants. Combined removal rates of 80.5 % for the dissolved organic carbon and 86.7 % for the biotoxicity in petrochemical wastewater were obtained with the enhanced two-step adsorption. The adsorption performance of both adsorbents remained stable even after five cycles. The selective adsorption mechanism revealed that hydrophobic organics such as DMF was adsorbed by the macropores of coal activated carbon, while the FDOM was eliminated by π-π stacking, electrostatic interaction and hydrophobic interaction. The hydrophilic organics were removed by the mesopores of aluminum silica gel, the silica hydroxyl groups and hydrophilic interaction. This study provides a comprehensive understanding of the selective adsorption mechanism and enhanced stepwise removal of multiple pollutants in petrochemical wastewater, which will guide the deep treatment of complex wastewater.

Advancing the development of nanocomposite adsorbent through zinc-doped nickel ferrite-pinecone biochar for removal of chromium (VI) from wastewater

Leather and textile industrial effluents are the main disseminating routes for chromium contamination of water bodies, causing adverse impacts on public and environmental health. The attempt to remediate chromium through conventional wastewater treatment methods is inefficient. Therefore, this study aims to synthesize zinc-doped nickel ferrite pinecone biochar (Zn-NiF@PBC) nanocomposite for the removal of chromium from wastewater systems. The Zn-NiF@PBC nanocomposite was synthesized via the co-precipitation method. The properties of zinc-doped nickel ferrite (Zn-NiF) were effectively modified by blending with biochar at 1, 5, 10, and 15 % (w/w) which was successfully embedded with Zn-Ni ferrite nanoparticles. This was characterized and confirmed by typical adsorbent properties such as a high surface area of 104 m2/g, conducive pore volume of 0.117 cm3/g and pore size of 3.41 nm (BET), interactive multi-functional groups (FTIR), surface charge determination (pHpzc,), crystalline structure (XRD) and very rough surface morphology (SEM). The maximum chromium adsorption was found to be 95 % at the specific experimental condition of pH 3, adsorbent dose 1 g/50 mL, contact time 120 min, and initial chromium concentration 100 mg/L. The adsorption experimental data was best fitted with the Langmuir isotherm at R2 0.98 indicating the adsorption process was homogeneous and monolayer whereas the kinetics adsorption was resembling the second-order kinetic at R2 0.99. Moreover, the adsorption thermodynamics was spontaneous, endothermic, and increased the change in entropy. Finally, the regeneration of Zn-NiF@PBC was found to be effective up to five 5 cycles but gradually degrading in terms of removal efficiency after 3 cycles. In general, Zn-NiF@PBC can remediate chromium from wastewater with huge potential for scale-up and extend to other pollutants clear-up.

Nanocomposite from tannery sludge-derived biochar and Zinc oxide nanoparticles for photocatalytic degradation of Bisphenol A toward dual environmental benefits

The growing concern over the presence of pollutants like Bisphenol A (BPA) in water sources has led to the growth of novel treatment technologies for its removal. This research work investigates the development of a novel biochar-metal oxide nanocomposite derived from tannery sludge and Zinc oxide (ZnO) nanoparticles for the photodegradation of BPA. The biochar was obtained by pyrolysis process, followed by impregnation of ZnO nanoparticles using a hydrothermal technique. The critical properties of as-prepared nanocomposite were evaluated by FT-IR, BET surface area, XRD, FE-SEM, HR-TEM, XPS, PL, EPR, and Raman Spectroscopy. In addition, the photocatalytic activity of nanocomposites was evaluated by measuring the degradation of BPA in visible light irradiation. The outcomes revealed that ZnO-loaded chemically activated biochar exhibited higher photocatalytic activity for the degradation of BPA than the pristine and non-chemically activated biochar. At pH 5, 0.2 g/L of photocatalyst dosage, 20 ppm of initial pollutant concentration, and 150 min of contact time, the maximum degradation efficiency of BPA was observed as 94.50 %. Also, nanocomposites showed good stability and reusability, with only a slight decrease in photocatalytic activity after multiple cycles of use. More importantly, the degradation mechanisms of BPA using as-prepared nanocomposites were analyzed in detail, indicating that the observed photocatalytic activity could be attributed to the synergistic effect between the biochar and ZnO, which provided a large surface area for the adsorption of BPA and promoted the generation of reactive oxygen species for its degradation. Overall, this study highlighted the potential of using nanocomposites from tannery sludge-derived biochar and ZnO nanoparticles for the degradation of BPA from polluted water sources using a photocatalytic process toward the dual environmental benefits.

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

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

Empowering Adsorption and Photocatalytic Degradation of Ciprofloxacin on BiOI Composites: A Material-by-Design Investigation

Binary and ternary composites of BiOI with NH2-MIL-101(Fe) and a functionalized biochar were synthesized through an in situ approach, aimed at spurring the activity of the semiconductor as a photocatalyst for the removal of ciprofloxacin (CIP) from water. Experimental outcomes showed a drastic enhancement of the adsorption and the equilibrium (which increased from 39.31 mg g-1 of bare BiOI to 76.39 mg g-1 of the best ternary composite in 2 h time), while the kinetics of the process was not significantly changed. The photocatalytic performance was also significantly enhanced, and the complete removal of 10 ppm of CIP in 3 h reaction time was recorded under simulated solar light irradiation for the best catalyst of the investigated batch. Catalytic reactions supported by different materials obeyed different reaction orders, indicating the existence of different mechanisms. The use of scavengers for superoxide anion radicals, holes, and hydroxyl radicals showed that although all these species are involved in CIP photodegradation, the latter play the most crucial role, as also confirmed by carrying out the reaction at increasing pH conditions. A clear correlation between the reduction of BiOI crystallite sizes in the composites, as compared to the bare material, and the material performance as both adsorbers and photocatalyst was identified.

Adsorptive removal of malachite green dye from aqueous solution using Rumex abyssinicus derived activated carbon

The potential for malachite green dye saturated effluent to severely affect the environment and human health has prompted the search for effective treatment technologies. Thus, this study was conducted with the goal of developing activated carbon from Rumex abyssinicus for the adsorptive removal of malachite green dye from an aqueous solution. Unit operations such as drying, size reduction, impregnation with H3PO4, and thermal activation were used during the preparation of the activated carbon. An experiment was designed considering four main variables at their respective three levels: initial dye concentration (50, 100, and 150 mg/L), pH (3, 6, and 9), contact period (20, 40, and 60 min), and adsorbent dosage (0.05, 0.01, and 0.15 g/100 mL). Optimization of the batch adsorption process was carried out using the Response Surface methodology's Box Behnken approach. The characterization of the activated carbon was described by SEM for surface morphology with cracks and highly porous morphology, FTIR for multi-functional groups O-H at 3506.74 cm-1 and 3290.70 cm-1, carbonyl group stretching from aldehyde and ketone (1900-1700 cm-1), stretching motion of aromatic ring C=C (1543.12 cm-1), stretching motion of -C-H (1500-1200 cm-1), vibrational and stretching motion of -OH (1250.79 cm-1), and vibrational motion of C-O-C (1049.32 cm-1), pHpzc of 5.1, BET for the specific surface area of 962.3 m2/g, and XRD for the presence of amorphous structure. The maximum and minimum dye removal efficiencies of 99.9% and 62.4% were observed at their respective experimental conditions of (100 mg/L, 0.10 mg/100 mL, pH 6, and 40 min) and (100 mg/L, 0.15 mg/100 mL, pH 3, and 20 min), respectively. Langmuir, Freundlich, Toth, and Koble-Corrigan models were used to evaluate the experimental data, in which Koble-Corrigan model was found to be the best fit with the highest value of R2 0.998. In addition to this, the kinetic studies were undertaken using pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Boyd models, and as a result, the pseudo-second-order model proved to have a better fit among the kinetic models. The kinetics and isotherm analysis revealed that the nature of the adsorption to be homogenous and monolayer surfaces driven by chemosorption. Furthermore, the thermodynamics study revealed the nature of adsorption to be feasible, spontaneous, and endothermic. On the other hand, the reusability study depicted the fact that the adsorbent can be utilized for five cycles with a negligible drop in the removal efficiencies from 99.9 to 95.2%. Finally, the low-cost, environmentally benign, and high adsorption capacity of the adsorbent material derived from Rumex abyssinicus stem could be used to treat industrial effluents.

2D/2D Biochar/Bi2WO6 Hybrid Nanosheets with Enhanced Visible-Light-Driven Photocatalytic Activities for Organic Pollutants Degradation

In this work, a novel two-dimensional/two-dimensional (2D/2D) hybrid photocatalyst consisting of Bi2WO6 (BWO) nanosheets and cotton fibers biochar (CFB) nanosheets was successfully prepared via a facile hydrothermal process. The as-prepared photocatalysts were characterized by a variety of techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. It was revealed that amorphous CFB nanosheets were uniformly immobilized on the surface of crystalline BWO nanosheets, and an intimate contact between CFB and BWO was constructed. The photocatalytic activities of the prepared BWO and CFB-BWO photocatalysts were evaluated by photocatalytic degradation of rhodamine B (RhB) and tetracycline hydrochloride (TC-HCl) in aqueous solutions under visible-light irradiation. Compared to the pristine BWO, the CFB-BWO composite photocatalysts exhibited significant enhancement in photocatalytic activities. Among all CFB-BWO samples, the 9CFB-BWO sample with the CFB mass ratio of 9% exhibited optimal photocatalytic activities for RhB or TC-HCl degradation, which was ca. 1.8 times or 2.4 times that of the pristine BWO, respectively. The improvement in photocatalytic activities of the CFB-BWO photocatalysts could be ascribed to the enhanced migration and separation of photogenerated charge carriers due to the formation of a 2D/2D interfacial heterostructure between CFB and BWO. Meanwhile, the possible mechanism of CFB-BWO for enhanced photocatalytic performance was also discussed. This work may provide a new approach to designing and developing novel BWO-based photocatalysts for the highly efficient removal of organic pollutants.

Preparation, characterisation and applications of bone char, a food waste-derived sustainable material: A review

The production of increasing quantities of by-products is a key challenge for modern society; their valorisation - turning them into valuable compounds with technological applications - is the way forward, in line with circular economy principles. In this review, the conversion of bones (by-products of the agro-food industry) into bone char is described. Bone char is obtained with a process of pyrolysis, which converts the organic carbon into an inorganic graphitic one. Differently from standard biochar of plant origin, however, bone char also contains calcium phosphates, the main component of bone (often hydroxyapatite). The combination of calcium phosphate and graphitic carbon makes bone char a unique material, with different possible uses. Here bone chars' applications in environmental remediation, sustainable agriculture, catalysis and electrochemistry are discussed; several aspects are considered, including the bones used to prepare bone char, the preparation conditions, how these affect the properties of the materials (i.e. porosity, surface area) and its functional properties. The advantages and limitations of bone chars in comparison to traditional biochar are discussed, highlighting the directions the research should take for bone chars' performances to improve. Moreover, an analysis on the sustainability of bone chars' preparation and use is also included.

Adsorption of chromium from electroplating wastewater using activated carbon developed from water hyacinth

Industrial wastewater polluted with high concentrations of Cr is commonly discharged into water resources without proper treatment. This gives rise to the deterioration of water quality and imposes adverse effects on public health. Therefore, this study is aimed at removing Cr from electroplating wastewater using activated carbon produced from water hyacinth under a full factorial experimental design with three factors and three levels (pH,2,5 and 8, adsorbent dose 0.5,1and1.5 in 100 mL and contact time 30, 60 and120 min). A phosphoric acid solution of 37% was used to activate the carbon, which was then subjected to thermal decomposition for 15 min at 500 °C. The activated carbon was characterized by the presence of a high surface area (203.83 m²/g) of BET, cracking of adsorbent beads of SEM morphology, amorphous nature of XRD, and many functional groups of FTIR such as hydroxyl (3283 cm^-1), alkane (2920 cm^-1), nitrile (2114 cm^-1) and aromatics (1613 cm^-1). The minimum Cr adsorption performance of 15.6% was obtained whereas maximum removal of 90.4% was recorded at the experimental condition of pH 2, adsorbent dose of 1.5 g/100 mL, and contact time of 120 min at a fixed value of initial Cr concentration of 100 mg/L. Similarly, the maximum Cr removal from real electroplating wastewater was 81.2% at this optimum point. Langmuir's model best described the experimental value at R² 0.96 which implies the adsorption is chemically bonded, homogeneous, and monolayer. Pseudo-second-order model best fits with the experimental data with R² value of 0.99. The adsorbent was regenerated for seven cycles and the removal efficiency decreased from 93.25% to 21.35%. Finally, this technology is promising to be scaled up to an industrial level.

Recent innovations and challenges in the eradication of emerging contaminants from aquatic systems

Presence of emerging pollutants (EPs), aka Micropollutants (MPs) in the freshwater environments is a severe threat to the environment and human beings. They include pharmaceuticals, insecticides, industrial chemicals, natural hormones, and personal care items and the pollutants are mostly present in wastewater generated from urbanization and increased industrial growth. Even concentrations as low as ngL^-1 or mgL^-1 have proven ecologically lethal to aquatic biota. For several years, the biodegradation of various Micropollutants (MPs) in aquatic ecosystems has been a significant area of research worldwide, with many chemical compounds being discovered in various water bodies. As aquatic biota spends most of their formative phases in polluted water, the impacts on aquatic biota are obvious, indicating that the environmental danger is substantial. In contrast, the impact of these contaminants on aquatic creatures and freshwater consumption is more subtle and manifests directly when disrupting the endocrine system. Research and development activities are expected to enable the development of ecologically sustainable, cost-effective, and efficient treatments for practical systems in the near future. Therefore, this review aims to understand recent emerging pollutants discovered and the available treatment technologies and suggest an innovative and cost-effective method to treat these EPs, which is sustainable and follows the circular bioeconomy.

Recent advances in spinel ferrite-based magnetic photocatalysts for efficient degradation of organic pollutants

Although spinel ferrite (MFe₂O₄, M = Zn, Ni, Mn, etc.) has been reported as a promising catalyst, its low photocatalytic activity under visible light greatly restricts its practical application. Spinel ferrite-based photocatalytic composites have exhibited improved efficiency for pollutant degradation, due to interface charge carrier mobility and structural modification. Meanwhile, due to its magnetism and stability, spinel ferrite composite can be easily recycled for long-term utilization, showing its high application potential. In this review, the recent advances in the construction and photocatalytic degradation of spinel ferrite composites are discussed, with an emphasis on the relationship between structural property and photocatalytic activity. In addition, to improve their photocatalytic application, the challenges, gaps and future research prospects are proposed.

Design of biomass-based composite photocatalysts for wastewater treatment: a review over the past decade and future prospects

This investigation applied a systematic review approach on publications covering primary data during 2012-2022 with a focus on photocatalytic degradation of pollutants in aqueous solution by composite materials synthesized with biomass and, at least, TiO₂ and/or ZnO semiconductors to form biomass-based composite photocatalysts (BCPs). After applying a set of eligibility criteria, 107 studies including 832 observations/entries were analyzed. The average removal efficiency and degradation kinetic rate reported for all model pollutants and BCPs were 77.5 ± 21.5% and 0.064 ± 0.174 min^-1, respectively. Principal component analysis (PCA) was applied to analyze BCPs synthesis methods, experimental conditions, and BCPs' characteristics correlated with the removal efficiency and photodegradation kinetics. The relevance of adsorption processes on the pollutants' removal efficiency was highlighted by PCA applied to all categories of pollutants (PCA_pol). The PCA applied to textile dyes (PCA_dyes) and pharmaceutical compounds (PCA_pharma) also indicate the influence of variables related to the composite synthesis (i.e., thermal treatment and time spent on BCPs synthesis) and photocatalytic experimental parameters (catalyst concentration, pollutant concentration, and irradiation time) on the degradation kinetic accomplished by BCPs. Furthermore, the multivariate analysis (PCA_pol) revealed that the specific surface area and the narrow band gap are key characteristics for BCPs to serve as a competitive photocatalyst. The effect of scavengers on pollutants' degradation and the recyclability of BCPs are also discussed, as necessary aspects for scalability trends. Further investigations are recommended to compare the performance of BCPs and commercial catalysts, as well as to assess the costs to treat real wastewater.

Synthesis of biochar-CoFe2O4 nanocomposite for adsorption of methylparaben from wastewater under full factorial experimental design

The presence of endocrine-disrupting chemicals in municipal wastewater has emerged as a threat to human health and the environment. Therefore, this study aimed to develop biochar-cobalt ferrite (BCF) nanocomposite for the removal of methylparaben from water under the full factorial experimental design of 4 factors with 3 levels (3⁴). The biochar-CoFe₂O₄ nanocomposite was developed by co-precipitation method from cobalt ferrite and biochar of Eucalyptus tree bark. Adsorbent surface morphology and functional and elemental composition were carried out by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and energy-dispersive X-ray spectroscopy (EDS) techniques which showed the presence of cracks with a rough surface, reasonable surface chemical composition, and many chemical functional groups, respectively. The experimental and predicted adsorption efficiencies ranged from 25.3 to 85.6% and 21.8 to 80.3%, respectively. The maximum adsorption performance (85.6%) reduced the methylparaben concentration from 27.5 to 4.0 mg/L at the optimum condition of adsorbent dose of 55 mg/100 mL, pH 6, contact time 90 min, and the initial methylparaben concentration of 27.5 mg/L. However, the adsorbent dose was the most influential main factor whereas the least influential was the interaction between solution pH and contact time under the regression model. The model also showed that 69% methylparaben removal was described by the regression model. The experimental data best fitted with the Freundlich model indicate multilayer adsorption which is the implication of physisorption. The sorption mechanism is attributed to Vander Waals forces, H-bonding, and dipole interaction. This BCF nanocomposite adsorbent appears to be promising for the removal of methylparaben from wastewater, but a further optimization process is essential to boost the treatment performance.

Visible-light-driven photocatalytic degradation of dye and antibiotics by activated biochar composited with K+ doped g-C3N4: Effects, mechanisms, actual wastewater treatment and disinfection

To improve the performance of graphitic carbon nitride (g-C₃N₄), a hotly researched metal-free photocatalyst, for better application in the efficient removal of organic pollutants, adsorption synergistically enhanced photocatalysis mechanism was thoroughly explored. Based on KOH pore-forming activated biochar (ACB) and K⁺ doped g-C₃N₄ (K-gC₃N₄), the novel activated biochar-based K-gC₃N₄ composite (ACB-K-gC₃N₄) was synthesized via the innovative ultrasonic-milling method. Rhodamine B (RhB), tetracycline (TC), norfloxacin (NOR), and chloramphenicol (CAP) were selected as target pollutants, and the effects of environmental factors, recycling and actual wastewater tests, disinfection effects, and various enhancement strategies were investigated. The results showed that K-gC₃N₄ was successfully composited with ACB by various characterizations, where the loading mass ratio of 1:2 exhibited the best performance. ACB-K-gC₃N₄ possessed a larger specific surface area, richer functional groups, suitable band gap (2.29 eV), and broader visible light absorption (~716 nm) than K-gC₃N₄. ACB-K-gC₃N₄ presented effective removal efficiency over K-gC₃N₄ for four pollutants, in which the removal efficiency of RhB reached 93.26%, and the degradation rate constant of 0.0119 min^-1 was four times higher than K-gC₃N₄ (0.0029 min^-1). Moreover, ACB-K-gC₃N₄ was superior to K-gC₃N₄ in disinfecting S. aureus and E. coli, with a sterilization rate of exceeding 90% for 12 h. The photodegradation activity was dominated by ·O₂^-, h⁺, and ·OH, and the mechanisms involved in the three stages. This was attributed to the unique structure and surface properties (defects and persistent free radicals) of ACB, as evidenced by improved adsorption stage and transfer of degradation intermediates, facilitated the generation of active species, accelerated migration of photogenerated electrons, and inhibited photogenerated carriers recombination by the heterojunction. The good reusability and stability, enhancement strategies (blowing air and heating), and satisfactory feasibility for actual wastewater allow ACB-K-gC₃N₄ possible to promote high-concentration wastewater treatment and disinfection.

Biochar Nanocomposite as an Inexpensive and Highly Efficient Carbonaceous Adsorbent for Hexavalent Chromium Removal

Biochar is commonly used for soil amendment, due to its excellent water-holding capacity. The Cr(VI) contamination of water is a current environmental issue in industrial regions. Here, we evaluated the effects of two-step modifications on boosting biochar's performance in terms of the removal of aqueous hexavalent chromium (Cr(VI)), along with investigating the alterations to its surface properties. The first modification step was heat treatment under air at 300 °C, producing hydrophilic biochar (HBC). The resulting HBC was then impregnated with zero-valent iron nanoparticles (nZVI), creating an HBC/nZVI composite, adding a chemical reduction capability to the physical sorption mechanism. Unmodified biochar (BC), HBC, and HBC/nZVI were characterized for their physicochemical properties, including surface morphology and elemental composition, by SEM/EDS, while functional groups were ascertained by FTIR and surface charge by zeta potential. Cr(VI) removal kinetic studies revealed the four-time greater sorption capacity of HBC than BC. Although unmodified BC showed faster initial Cr(VI) uptake, it rapidly worsened and started desorption. After nZVI impregnation, the Cr(VI) removal rate of HBC increased by a factor of 10. FTIR analysis of biochars after Cr(VI) adsorption showed the presence of Cr(III) oxide only on the used HBC/nZVI and demonstrated that the carbonyl and carboxyl groups were the main groups involved in Cr(VI) sorption. Modified biochars could be considered an economical substitute for conventional methods.