Photocatalytic behavior of biochar-modified carbon nitride with enriched visible-light reactivity

Multi-active photocatalysts of biochar-doped g-C3N4 incorporated with polyoxometalates for the high-efficient degradation of sulfamethoxazole

Sulfamethoxazole (SMX) is one of major antibiotic contaminants in current aqueous environment. In this paper, waste loofah and melamine were co-carbonized to prepare biochar-doped g-C3N4 (CCN) by a one-pot method and then combined with Co2PMo11VO40 (CoPMoV) using a binder to obtain the novel polyoxometalates (POMs) photocatalytic composites (CCN/CoPMoV). The incorporation of CoPMoV dramatically reduced the photogenerated carrier recombination and led to a small band gap. Under visible light, the synergetic activation from biochar, g-C3N4 and POMs can remove 98.5% of SMX (k = 0.215 min-1) in the peroxymonosulfate (PMS) system within 20 min and keep its high stability with the degradation of 88.9% after five cycles. Multi-active sites from CCN/CoPMoV are contributed to develop the most active species of , ·OH, 1O2, and h+. The validity in the degradation of SMX makes CCN/CoPMoV a promising and potential material for the removal of aqueous pollutants in the future.

A comprehensive review of the "black gold catalysts" in wastewater treatment: Properties, applications and bibliometric analysis

A significant amount of effort has been devoted to the utilization of biochar-based catalysts in the treatment of wastewater. By virtue of its abundant functional groups and high specific surface area, biochar holds significant promise as a catalyst. This article presents a comprehensive systematic review and bibliometric analysis covering the period from 2009 to 2024, focusing on the restoration of wastewater through biochar catalysis. The production, activation, and functionalization techniques employed for biochar are thoroughly examined. In addition, the application of advanced technologies such as advanced oxidation processes (AOPs), catalytic reduction reactions, and biochemically driven processes based on biochar are discussed, with a focus on elucidating the underlying mechanisms and how surface functionalities influence the catalytic performance of biochar. Furthermore, the potential drawbacks of utilizing biochar are also brought to light. To emphasize the progress being made in this research field and provide valuable insights for future researchers, a scientometric analysis was conducted using CiteSpace and VOSviewer software on 595 articles. Hopefully, this review will enhance understanding of the catalytic performance and mechanisms pertaining to biochar-based catalysts in pollutant treatment while providing a perspective and guidelines for future research and development efforts in this area.

Novel Approach to Photocatalytic Removal of Linezolid by Advanced Nano-Biochar/Bismuth Oxychloride Hybrid

Herein, we introduce an innovative nanohybrid material for advanced wastewater treatment, composed of Corchorus olitorius-derived biochar and bismuth oxychloride (Biochar/Bi12O17Cl2), demonstrated in a solar photoreactor. This work focuses on the efficient degradation of linezolid (LIN), a persistent pharmaceutical pollutant, utilizing the unique (photo)catalytic capabilities of the nanohybrid. Compared with its individual components, the biochar/Bi12O17Cl2 hybrid exhibits a remarkable degradation efficiency of 82.6% for LIN, alongside significant chemical oxygen demand (COD) and total organic carbon (TOC) mineralization rates of 81.3 and 75.8%, respectively. These results were achieved within 3 h under solar irradiation, using an optimal composite dose of 125 mg/L at pH 4.3 ± 0.45, with an initial COD and LIN concentrations of 1605 and 160.8 mg/L and TOC of 594.3 mg/L. The nanohybrid's stability across five cycles of use demonstrates its potential for repeated applications, with degradation efficiencies of 82.6 and 77.9% in the first and fifth cycles, respectively. This indicates the biochar/Bi12O17Cl2 composite's suitability as a sustainable and cost-effective solution for the remediation of heavily contaminated waters. Further, the degradation pathway proposed the degradation of all of the generated intermediates to a single-ring compound. Contributing to the development of next-generation materials for environmental remediation, this research underscores the critical role of nanotechnology in enhancing water quality and ecosystem sustainability and addressing the global imperative for clean water access and environmental preservation.

Graphitic-carbon-nitride-hydrophilicity-dependent photocatalytic degradation of antibiotics with different log Kow

The surface hydrophilicity of a photocatalyst is an important factor that directly influences its interactions with organic pollutants and significantly impacts its degradation. In this study, we investigated the impact of increased hydrophilicity of g-C3N4 (CN) by alkaline solvothermal treatment on the degradations of three antibiotics (oxytetracycline (OTC), oxolinic acid (OA), and sulfamethoxazole (SMX)) with different log Kow values. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Fourier-transform infrared (FT-IR) spectroscopy showed no significant differences in the morphology, crystalline structure, and surface functional groups of CN after alkaline solvothermal treatment (Nv-HPCN). However, contact angle analysis revealed that Nv-HPCN (31.8°) was more hydrophilic than CN (61.1°). To assess the hydrophilicity of the antibiotics, the log Kow values of SMX (0.77), OA (0.43), and OTC (-0.34) were measured. Nv-HPCN showed faster OTC degradation than CN, whereas the opposite pattern was observed for the degradation of OA. Scavenger tests showed that O2•- and h+ mainly contributed to the degradation of these antibiotics. Furthermore, the influences of NOM and coexisting anions on antibiotic degradation were investigated. This study thus offers perspectives on the impact of surface hydrophilicity of photocatalysts on the degradation of antibiotics.

Renewable Carbonaceous Materials from Biomass in Catalytic Processes: A Review

This review paper delves into the diverse ways in which carbonaceous resources, sourced from renewable and sustainable origins, can be used in catalytic processes. Renewable carbonaceous materials that come from biomass-derived and waste feedstocks are key to developing more sustainable processes by replacing traditional carbon-based materials. By examining the potential of these renewable carbonaceous materials, this review aims to shed light on their significance in fostering environmentally conscious and sustainable practices within the realm of catalysis. The more important applications identified are biofuel production, tar removal, chemical production, photocatalytic systems, microbial fuel cell electrodes, and oxidation applications. Regarding biofuel production, biochar-supported catalysts have proved to be able to achieve biodiesel production with yields exceeding 70%. Furthermore, hydrochars and activated carbons derived from diverse biomass sources have demonstrated significant tar removal efficiency. For instance, rice husk char exhibited an increased BET surface area from 2.2 m2/g to 141 m2/g after pyrolysis at 600 °C, showcasing its effectiveness in adsorbing phenol and light aromatic hydrocarbons. Concerning chemical production and the oxidation of alcohols, the influence of biochar quantity and pre-calcination temperature on catalytic performance has been proven, achieving selectivity toward benzaldehyde exceeding 70%.

A novel immobilized horseradish peroxidase platform driven by visible light for the complete mineralization of sulfadiazine in water

A novel immobilized enzyme driven by visible light was prepared and used for complete mineralization of antibiotics in water bodies. The immobilized enzyme was composed of carbon nitride modified by biochar (C/CN) and horseradish peroxidase (HRP), establishing the photo-enzyme coupling system with synergistic effect. Among them, the introduction of biochar not only improves the stability and loading capacity of the enzyme, but also improves the light absorption capacity and carrier separation efficiency of the photocatalyst. After the optimization of immobilization process, the solid load of HRP could reach 251.03 mg/g, and 85.03 % enzyme activity was retained after 18 days of storage at 4 °C. In the sulfadiazine (SDZ) degradation experiment, the degradation rate of HRP/C3/CN reached 71.21 % within 60 min, which was much higher than that of HRP (2.33 %), CN (49.78 %) and C3/CN (58.85 %). In addition, under the degradation of HRP/C/CN, the total organic carbon (TOC) removal rate of SDZ reached 53.14 %, which was 6.47 and 1.74 times that of CN and C3/CN, respectively. This study shows that the introduction of biochar is of great significance to the photo-enzyme cascade coupling system and provides a new strategy for the application of HRP&g-C3N4 system in wastewater treatment.

Different photoreduction processes of Cr(VI) on cellulose-rich and lignin-rich biochar

In this study, a series of biochar were prepared via pyrolyzing cellulose-rich pakchoi (PBC) and lignin-rich corncob (CBC) to explore the photoreduction process of Cr(VI). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy confirmed higher oxygenated functional groups in PBC (48.9%-57.1%), whereas CBC exhibited more aromatization properties due to the stable aromatic network in lignin. For PBC, the valence bands decreased from 1.42 eV to 1.20 eV with the increase of pyrolysis temperature from 300 °C to 500 °C; however, an opposite trend was observed for CBC. The photoreduction of Cr(VI) clearly showed that both PBC and CBC had the best performance at the carbonization temperature of 300 °C (named PBC300 and CBC300). It is noted that PBC300 exhibited the most effective photoreduction of Cr(VI), which was about 1.3 times higher than that of CBC300. The maximum reduction capacities of Cr(VI) were 68.2 mg g-1 on PBC300 and 66.1 mg g-1 on CBC300 at pH∼2.0. Compared with the insoluble char substances, dissolved black carbons made more contributions for Cr(VI) photoreduction, ∼70% in PBC and almost 100% in CBC, which suggested that in the case of PBC, the insoluble char and the corresponding dissolved black carbons play an important role in the photoreduction of Cr(VI). However, only dissolved black carbons contributed to Cr(VI) photoreduction on CBC. As the key reaction pathway, the interfacial electron transport dominated Cr(VI) reduction on PBC and CBC. Moreover, the radical of •O2- had some contribution to the reduction of Cr(VI) only in the PBC system. Interestingly, •OH could promote the photoreduction of Cr(VI) in both PBC and CBC systems, which might be due to the fact that •OH facilitated the formation of small molecule fragments. These findings provide an essential basis for evaluating the environmental impact of photocatalytic behaviors of biochar.

Adsorbed copper on urea modified activated biochar catalyzed H2O2 for oxidative degradation of sulfadiazine：Degradation mechanism and toxicity assessment

The combined pollution of heavy metals and organic compounds usually occurs simultaneously and induces high toxicity. The technology of simultaneous removal of combined pollution is lacking and the removal mechanism is not clear. Sulfadiazine (SD), a widely used antibiotic, was used as a model contaminant. Urea modified sludge-based biochar (USBC) was prepared and used to catalyze H₂O₂ to remove the combined pollution of Cu²⁺ and sulfadiazine (SD) without causing secondary pollution. After 2 h, the removal rates of SD and Cu²⁺ were 100 and 64.8%, respectively. Cu²⁺ adsorbed on the surface of USBC accelerated the activation of H₂O₂ by the USBC catalyzed by CO bond to produce hydroxyl radical (^•OH) and single oxygen (¹O₂) to degrade SD. Twenty-three intermediate products were detected, most of which were completely decomposed into CO₂ and H₂O. The toxicity was significantly reduced in the combined polluted system. This study highlights the potential of the low-cost technology based on sludge reuse and its inherent significance in reducing the toxic risk of combined pollution in the environment.

A novel BC/g-C3N4 porous hydrogel carrier used in intimately coupled photocatalysis and biodegradation system for efficient removal of tetracycline hydrochloride in water

Intimately coupled photocatalysis and biodegradation (ICPB) is a promising technology to remove refractory contaminants from water. The key to successful ICPB is a carrier capable of accumulating biofilm and adhering photocatalyst firmly. Herein, BC/g-C₃N₄ was prepared into a three dimensional porous hydrogel and used as a carrier in ICPB system for the first time. Degradation experiments revealed that the removal rate of tetracycline hydrochloride (TCH) in water by the ICPB system was 96.0% after 10 h, which was significantly higher than that by the photocatalysis (PC, 76.3%), biodegradation (B, 32.5%), adsorption (AD, 17.2%), and photolysis (P, 5.0%) systems. Photo-electrochemical tests confirmed that ICPB system had superior electron transfer ability between photocatalysts and microorganisms. The removal efficiency of COD proved that microorganisms played an important role in the mineralization process of TCH by the ICPB system. After the ICPB degradation experiment, microorganisms maintained high activity and Pseudomonas, Burkholderiaceae and Flavobacterium which had TCH degradation or electron transport ability, were enriched. In conclusion, the novel ICPB carrier overcame shortcomings of the traditional ICPB carrier and the novel ICPB system had superior degradation performance for TCH. This study provided a possible method to promote the practical application of ICPB technology.

Adsorption and photodegradation of reactive red 120 with nickel-iron-layered double hydroxide/biochar composites

Layered double hydroxide (LDH) materials were widely applied for adsorption and photodegradation of pollutants for wastewater treatment. New efficient LDH materials with adsorption and photodegradation abilities will be promising candidates for pollutants removal. Hence, a series of NiFe-LDH/biochar (NiFe/BC) were fabricated by the coprecipitation method for synergistic adsorption and photodegradation anionic dyes of reactive red 120 (RR120). The removal experiment showed that the addition of an appropriate amount of biochar into NiFe-LDH enhanced the adsorption capacity and its photocatalytic ability. The optimized NiFe/BC2 composite can remove 88.5 % of RR120 under visible light by adsorption and photocatalysis, which was much better than NiFe-LDH (63.3 %) and biochar (2.6 %). The photodegradation kinetic constant of the NiFe/BC2 composite was 3.1 and 104.8 times that of NiFe-LDH and BC. In addition, active species capture experiments and electron spin resonance (ESR) tests revealed the removal mechanisms of NiFe/BC composites for RR120 removal. This work affords a feasible strategy for preparing LDH-based photocatalyst with excellent adsorption and photocatalytic performance for wastewater treatment.

The effects of g-C3N4/biochar and g-C3N4 on bacterial community in riverbed sediment

Biochar had been widely used to improve the activity of photocatalysts, the biochar-based photocatalysts had more potential for environmental pollution remediation, but their effect on the sediment remained unknown. To understand these, the typical photocatalyst g-C₃N₄ was modified by biochar to develop g-C₃N₄/biochar with enhanced photocatalytic ability. Riverbed sediment was exposed to g-C₃N₄ and g-C₃N₄/biochar respectively for 30 days, and Illumina sequencing was utilized to examine the changes in the bacterial community in the sediment. The results showed that in riverbed sediment, g-C₃N₄ exposure had a concentration-dependent effect on the diversity of bacteria, while g-C₃N₄/biochar exposure had a slight influence on the bacterial diversity and the diversity almost maintained stable with different g-C₃N₄/biochar concentration. The application of g-C₃N₄ exhibited an inhibition influence on the growth of Acidobacteria, Gemmatimonadetes, and Rokubacteria in sediment, whose relative abundance increased when g-C₃N₄ was 25 mg/kg, and then decreased when g-C₃N₄ beyond this concentration. The presence of g-C₃N₄/biochar increased the relative abundance of Cyanobacteria in sediment and showed no obvious impact on other dominant phyla. Both g-C₃N₄ and g-C₃N₄/biochar could alter the levels of TP, NN, and AN in the sediment, but the magnitude of the changes of these physicochemical factors caused by g-C₃N₄/biochar was much smaller than those caused by g-C₃N₄. In addition, the complexity of the bacterial community network was reduced in a high concentration of g-C₃N₄, while it remained stable with different concentrations of g-C₃N₄/biochar treatments. Totally, this study demonstrated that, compared to g-C₃N₄, g-C₃N₄/biochar was able to maintain the relative stability of the bacterial community in riverbed sediment and mitigate the negative effects of photocatalysts to some extent, making biochar an ecological remediation agent with great potential for application.

Kitchen-waste-derived biochar modified nanocomposites with improved photocatalytic performances for degrading organic contaminants

Kitchen-waste-derived biochar (KBC) was produced by thermal treatment at 400 °C, and a series of KBC/BiOX (X = Br, Cl) photocatalysts were developed using ultrasonication and solvothermal treatment. The as-prepared photocatalysts were characterized by several tests and investigated by photocatalytic reactions towards methyl orange (MO) and tetracycline (TC). The best photocatalysts, 0.15KBC/BiOBr and 0.15KBC/BiOCl separately achieved complete MO photodegradation in 20 min and 35 min. Further study confirmed that 0.15KBC/BiOBr and 0.15KBC/BiOCl possessed excellent photocatalytic efficiency that was 17.9 and 14.8 times higher than BiOBr and BiOCl, respectively. In addition, 0.15KBC/BiOX showed higher activity removal of TC than pure BiOX in 60 min. Notably, 0.15KBC/BiOX maintained a reproducible high photocatalytic efficiency after five recycles. Estimated band gap energy for 0.15KBC/BiOBr (2.40 eV) and 0.15KBC/BiOCl (3.00 eV) was considerably lower than that of BiOBr (2.73 eV) and BiOCl (3.30 eV), indicating a delocalized state was created when forming electronic pathways on the interface. Besides, visible-light harvesting of photocatalysts got promoted by the modification of KBC. Active species trapping experiments and electron paramagnetic resonance (EPR) tests illustrated that photogenerated holes were the principal active species, while ∙OH was involved in the reaction. The successful synthesis of 0.15KBC/BiOX catalyst provided a new approach on simultaneously degrading organic contaminants in water and disposing of excessive kitchen waste.

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

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

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.

Integration of biochar into Ag3PO4/α-Fe2O3 heterojunction for enhanced reactive oxygen species generation towards organic pollutants removal

A biochar (BC) harbored Ag₃PO₄/α-Fe₂O₃ type-Ⅰ heterojunction (Ag-Fe-BC) was prepared by a hydrothermal-impregnation method to transfer active center of heterojunctions. The electrochemical and spectroscopic tests demonstrated that BC enhanced the catalytic performance of the heterojunction by enhancing photocurrent, reducing fluorescence intensity, and facilitating separation of electron-hole pairs. The photocatalytic activity showed the Ag-Fe-BC (5:1:3) could degrade Rhodamine B (20 mg/L) by up to 92.7%, which was 3.35 times higher than Ag₃PO₄/α-Fe₂O₃. Tetracycline and ciprofloxacin (20 mg/L) were degraded efficiently by 58.3% and 79.4% within 2 h, respectively. Electron paramagnetic resonance and scavenging experiments confirmed the major reactive oxygen species (ROS) consisted of singlet oxygen (¹O₂) and superoxide (·O₂^-). Excellent RhB adsorption and electrons capturing capacity of BC facilitated electron-hole pairs separation and ROS transferring to target organics followed by elevated degradation. Thus, a facile method was proposed to synthesize a highly efficient visible-light responsive photocatalyst for degradation of various organics in water.

Periodate activated by manganese oxide/biochar composites for antibiotic degradation in aqueous system: Combined effects of active manganese species and biochar

Developing efficient catalysts for oxytetracycline (OTC) degradation is an ideal strategy to tackle environmental pollution, and advanced oxidation processes (AOPs) have been widely used for its degradation. However, the studies on the activation of periodate (PI) by biochar and its composites in recent years have been scarcely reported. In this study, we focused on the degradation of OTC by PI activation with manganese oxide/biochar composites (Mn_xO_y@BC). Experimental results showed that the OTC degradation rate of Mn_xO_y@BC/PI system reached almost 98%, and the TOC removal efficiency reached 75%. Various characteristic analysis proved that PI could be activated efficiently by surface functional groups and manganese-active species (Mn(II), Mn(III), and Mn(IV)) on biochar, and various reactive species such as singlet oxygen (¹O₂), hydroxyl radical (∙OH), and superoxide radical (O₂^∙-) can be observed via radical quenching experiments. Based on this, three degradation pathways were proposed. Furthermore, Mn_xO_y@BC and PI were combined to degrade environmental pollutants, which achieved excellent practical benefits and had great practical application potential. We hope that it can provide new ideas for advanced oxidation processes (AOPs) applying for wastewater treatment in the future.

Enhanced Sonocatalytic Performance of Non-Metal Graphitic Carbon Nitride (g-C3N4)/Coconut Shell Husk Derived-Carbon Composite

This study focused on the modification of graphitic carbon nitride (g-C3N4) using carbon which was obtained from the pyrolysis of coconut shell husk. The sonocatalytic performance of the synthesized samples was then studied through the degradation of malachite green. In this work, pure g-C3N4, pure carbon and carbon/g-C3N4 composites (C/g-C3N4) at different weight percentages were prepared and characterized by using XRD, SEM-EDX, FTIR, TGA and surface analysis. The effect of carbon amount in the C/g-C3N4 composites on the sonocatalytic performance was studied and 10 wt% C/g-C3N4 showed the best catalytic activity. The optimization study was conducted by using response surface methodology (RSM) with a central composite design (CCD) model. Three experimental parameters were selected in RSM including initial dye concentration (20 to 25 ppm), initial catalyst loading (0.3 to 0.5 g/L), and solution pH (4 to 8). The model obtained was found to be significant and reliable with R2 value (0.9862) close to unity. The degradation efficiency of malachite green was optimized at 97.11% under the conditions with initial dye concentration = 20 ppm, initial catalyst loading = 0.5 g/L, solution pH = 8 after 10 min. The reusability study revealed the high stability of 10 wt% C/g-C3N4 as sonocatalyst. In short, 10 wt% C/g-C3N4 has a high potential for industrial application since it is cost effective, reusable, sustainable, and provides good sonocatalytic performance.

MOF-derived biochar composites for enhanced high performance photocatalytic degradation of tetracycline hydrochloride

Biochar reinforced advanced nanocomposites are of interest to a wide circle of researchers. Herein, we describe a novel MOF-derived reinforced cow dung biochar composite, which was prepared by a one-step hydrothermal method to form the MOF MIL-125(Ti) onto a nitrogen and sulfur co-doped bio-carbon (NSCDBC). The UV-vis diffuse reflectance spectrum of NSCDBC/MIL-125(Ti) exhibits an extension of light absorption in the visible region (360–800 nm), indicating its higher visible light capture capacity relative to pure MIL-125(Ti). The photocatalytic activity results show that all the NSCDBC/MIL-125(Ti) composite samples, namely NSCM-5, NSCM-10, NSCM-20 and NSCM-30 display good performance in the removal of tetracycline hydrochloride compared to pure MIL-125(Ti). Among them, NSCM-20 exhibits the highest catalytic activity with a removal rate of 94.62%, which is attributed to the excellent adsorption ability of NSCDBC and the ability to inhibit the complexation of photogenerated electron–hole pairs. Photoluminescence verifies that the loading of biochar successfully enhances the separation of photogenerated electron–hole pairs. Subsequently, the active species in the photocatalytic process are identified by using electron spin resonance spin-trap techniques and free radical trapping experiments. Finally, the possible reaction mechanism for the photocatalytic process is revealed. These results confirm that NSCDBC/MIL-125(Ti) is a potentially low-cost, green photocatalyst for water quality improvement.

Schematic diagram of fabricating process of NSCDBC/MIL-125(Ti).

In-situ synthesis of biochar modified PbMoO4: An efficient visible light-driven photocatalyst for tetracycline removal

For highly efficient photocatalytic remediation of organic pollutants, broad-spectrum light response and effective charge separation are two key goals. To achieve these goals, a novel biochar (BC) modified PbMoO₄ composite catalyst was successfully synthesized in situ by combining coprecipitation with pyrolysis treatment of poplar sawdust and the technical feasibility of degradation of tetracycline (TC) with compound photocatalyst prepared from recovered agricultural and forestry residues was preliminarily demonstrated. The characterization demonstrated that the presence of BC narrowed the bandgap, enhanced visible light absorption as well as facilitated charge separation. Three composites (with the mass ratio of PbMoO₄ to BC = 1:4; 1:1; and 4:1, respectively) displayed higher activity than pure PbMoO₄. The results showed that the composite with the PbMoO₄ to BC ratio of 1:4 exhibited the best photocatalytic activity, for 150 mg L^-1 TC the removal rate was 61.0%, and the rate constant was 8.1 × 10^-3 min^-1, while the photocatalytic activity of PbMoO₄ was 26.0% and 3.9 × 10^-3 min^-1. The reactions in the presence of radical quenchers indicated that holes (h⁺) and superoxide radicals (O₂^-) were the dominant active species for photodegradation. In different water matrices, for 150 mg L^-1 TC solution the photocatalytic activity of optimal photocatalyst decreased as follows: ultrapure water > artificial sewage > farm sewage > municipal sewage. Moreover, the catalyst exhibited good stability over five cycles. Therefore, BC doped PbMoO₄ provides a useful strategy for improving the photocatalytic ability of PbMoO₄-based photocatalysts and offers a promising method for water purification.

Nitrogen-Doped Porous Carbon Materials Derived from Graphene Oxide/Melamine Resin Composites for CO2 Adsorption

CO₂ adsorption in porous carbon materials has attracted great interests for alleviating emission of post-combustion CO₂. In this work, a novel nitrogen-doped porous carbon material was fabricated by carbonizing the precursor of melamine-resorcinol-formaldehyde resin/graphene oxide (MR/GO) composites with KOH as the activation agent. Detailed characterization results revealed that the fabricated MR(0.25)/GO-500 porous carbon (0.25 represented the amount of GO added in wt.% and 500 denoted activation temperature in °C) had well-defined pore size distribution, high specific surface area (1264 m²·g⁻¹) and high nitrogen content (6.92 wt.%), which was mainly composed of the pyridinic-N and pyrrolic-N species. Batch adsorption experiments demonstrated that the fabricated MR(0.25)/GO-500 porous carbon delivered excellent CO₂ adsorption ability of 5.21 mmol·g⁻¹ at 298.15 K and 500 kPa, and such porous carbon also exhibited fast adsorption kinetics, high selectivity of CO₂/N₂ and good recyclability. With the inherent microstructure features of high surface area and abundant N adsorption sites species, the MR/GO-derived porous carbon materials offer a potentially promising adsorbent for practical CO₂ capture.

Adsorption and visible-light photocatalytic degradation of organic pollutants by functionalized biochar: Role of iodine doping and reactive species

Here we developed the functionalized biochar as low-cost and heavy metal-free photocatalysts via a facile iodine doping method, which exhibit efficient adsorption and visible-light-driven photocatalytic degradation of representative organic pollutants, phenol and tetracycline. On one hand, iodine doping elevates the adsorption via creating extra pores, e.g., the adsorbed amounts of phenol by iodine-doped WSP and OSR biochar are increased by 161.8% and 146.3%, respectively, which in turn facilitates the photocatalytic oxidation of the adsorbed pollutants. On the other hand, iodine doping leads to the strong photo-induced excitation and remarkably reduced charge carrier transfer resistance, boosting the photocatalytic activity of iodine-doped biochar by more than 20 orders towards organic pollutants (e.g., phenol) degradation. The systematic analysis of reactive species reveals the active roles of O₂^-, H₂O₂, ¹O₂, OH, electrons, and holes in photocatalytic process and identifies O₂^- to be the major contributor. This work affords a facile approach to generating porous and visible-light-driven photocatalyst from biomass for efficient adsorbing and degrading organic pollutants, opening up an avenue to turn biowaste into biomaterials for sustainable environmental remediation.

Enhanced photocatalytic degradation of methyl orange by coconut shell-derived biochar composites under visible LED light irradiation

The conversion of carbon-rich biomass into valuable material is an environmental-friendly approach for its reutilization. In this study, coconut shell-derived biochar, graphitic carbon nitride (g-C₃N₄), g-C₃N₄/biochar, titanium dioxide (TiO₂)/biochar, zinc oxide (ZnO)/biochar, and ferric oxide (Fe₂O₃)/biochar were synthesized and characterized by using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), surface area analysis, UV-Vis diffuse reflectance spectroscopy (DRS), and zeta potential analysis. The g-C₃N₄ or metal oxide particles were found to be well-distributed on the coconut shell-derived biochar with the improvement in thermal stability and enlargement of specific surface area. A great reduction in band gap energy was observed in the composite materials after incorporating with the biochar. Among different biochar composites, g-C₃N₄/biochar was found to have the highest photocatalytic activity. The interactive effect of parameters such as catalyst dosage, peroxymonosulfate (PMS) oxidant dosage, and solution pH on the photocatalytic degradation of methyl orange was investigated using the response surface methodology (RSM). The highest photocatalytic degradation efficiency (96.63%) was achieved at catalyst dosage of 0.75 g/L, oxidant dosage of 0.6 mM, and solution pH 3 after 30 min.

Z-scheme Au decorated carbon nitride/cobalt tetroxide plasmonic heterojunction photocatalyst for catalytic reduction of hexavalent chromium and oxidation of Bisphenol A

Au/g-C₃N₄/Co₃O₄ plasmonic heterojunction photocatalyst was successfully prepared by in-situ forming Co₃O₄ nanocubes on the Au/g-C₃N₄ nanosheets. The catalytic activities of the photocatalysts were systematically studied through the catalytic reduction of hexavalent chromium (Cr⁶⁺) and oxidation of Bisphenol A (BPA) under visible light irradiation, while according to the degradation products determined by GC-MS, the catalytic degradation pathway of BPA was proposed. 4Au/g-C₃N₄/Co₃O₄ sample exhibits the most efficient catalytic activities, and the photocatalytic reduction and photocatalytic oxidation efficiencies can obtain 85.6% and 90.3%, respectively. The main reasons of the enhancing catalytic performance are the high absorption capability to visible light generated by localized surface plasmon resonance and the effective interface charge separation. Finally, we speculated that the Au/g-C₃N₄/Co₃O₄ sample followed Z-scheme charge transfer mechanism in this study, which is verified by the analysis of experiment and theoretical calculation results.

Graphitic carbon nitride/biochar composite synthesized by a facile ball-milling method for the adsorption and photocatalytic degradation of enrofloxacin

In order to enhance the removal performance of graphitic carbon nitride (g-C₃N₄) on organic pollutant, a simultaneous process of adsorption and photocatalysis was achieved via the compounding of biochar and g-C₃N₄. In this study, g-C₃N₄ was obtained by a condensation reaction of melamine at 550°C. Then the g-C₃N₄/biochar composites were synthesized by ball milling biochar and g-C₃N₄ together, which was considered as a simple, economical, and green strategy. The characterization of resulting g-C₃N₄/biochar suggested that biochar and g-C₃N₄ achieved effective linkage. The adsorption and photocatalytic performance of the composites were evaluated with enrofloxacin (EFA) as a model pollutant. The result showed that all the g-C₃N₄/biochar composites displayed higher adsorption and photocatalytic performance to EFA than that of pure g-C₃N₄. The 50% g-C₃N₄/biochar performed best and removed 45.2% and 81.1% of EFA (10 mg/L) under darkness and light with a dosage of 1 mg/mL, while g-C₃N₄ were 19.0% and 27.3%, respectively. Besides, 50% g-C₃N₄/biochar showed the highest total organic carbon (TOC) removal efficiency (65.9%). Radical trapping experiments suggested that superoxide radical (•O₂^-) and hole (h⁺) were the main active species in the photocatalytic process. After 4 cycles, the composite still exhibited activity for catalytic removal of EFA.

Enhanced heterogeneous photo-Fenton-like degradation of tetracycline over CuFeO2/biochar catalyst through accelerating electron transfer under visible light

The visible-light induced heterogeneous photo-Fenton-like (HPF-like) process is regarded as a promising technique for organic pollutants degradation due to its efficient utilization of solar energy and high H₂O₂ activation activity. This study prepared the CuFeO₂/biochar catalysts via hydrothermal technique at no extra reductant and systematically investigated their band structure and photoelectric properties. The dispersed distribution of CuFeO₂ particles in CuFeO₂/biochar composites narrowed bandgap of CuFeO₂ and promoted electron transport of CuFeO₂. Compared with CuFeO₂, the CuFeO₂/biochar containing 1.0 g biochar in the preparation (CuFeO₂/biochar-1.0) possessed higher carrier density and longer photoelectron lifetime, which is beneficial to higher catalytic performance. The apparent rate constant for tetracycline as target pollutant degradation by CuFeO₂/biochar-1.0 was 2.0 times higher than that by CuFeO₂. The acquired optimum conditions for tetracycline degradation were 220 mg L^-1 CuFeO₂/BC-1.0, 22 mM H₂O₂ and pH 6.4 using response surface methodology. The quenching experiments and ESR analysis revealed that OH was the predominant active species, and photoelectron and O₂^- were auxiliary species. The photoelectron could promote in-situ recycling of Cu²⁺ to Cu⁺ and Fe³⁺ to Fe²⁺, which significantly improved H₂O₂ activation by CuFeO₂. The possible pathway of tetracycline was proposed according to intermediates identified by HPLC/MS. The toxicity analysis demonstrated that the overall toxicity of the identified intermediates was reduced in HPF-like system.

Study on the Photocatalysis Mechanism of the Z-Scheme Cobalt Oxide Nanocubes/Carbon Nitride Nanosheets Heterojunction Photocatalyst with High Photocatalytic Performances

An efficient Z-scheme Co₃O₄/g-C₃N₄ heterojunction photocatalyst was developed via in-situ forming Co₃O₄ nanocubes on the g-C₃N₄ nanosheet in the hydrothermal process. The obtained photocatalyst exhibited high photocatalytic activity for the visible-light-driven catalytic reduction of Cr(VI) and catalytic oxidation of tetracycline (TC). Among the as-synthesized catalysts, Co₃O₄/g-C₃N₄-0.04 (the mass ratio of g-C₃N₄ to Co₃O₄ is 0.04) sample exhibits the most efficient catalytic activities. The photocatalytic reduction and photocatalytic oxidation efficiencies of Co₃O₄/g-C₃N₄-0.04 can obtain 81.3 and 92.6 %, respectively. Moreover, the TC is mineralized in the course of photocatalytic degradation, 72.2% of TOC is removed from the reaction system. In addition, the apparent quantum efficiency for the removal of Cr(VI) was also obtained and the the Co₃O₄/g-C₃N₄-0.04 could achieve the highest apparent quantum efficiency among the samples. The enhancing photocatalytic activities originated from the efficient interfacial charge migration and separation obtained in Co₃O₄/g-C₃N₄-0.04, which is preliminarily confirmed by the photoluminescence spectra, time-resolved photoluminescence spectra and the photoelectrochemical characterizations. Finally, we speculate that the Co₃O₄/g-C₃N₄ heterostructures follow a more reasonable Z-scheme charge transfer in this study, which is confirmed by analyzing the results of electron paramagnetic resonance, radical scavenging experiments, and theoretical calculations.

Insights into the photocatalysis mechanism of the novel 2D/3D Z-Scheme g-C3N4/SnS2 heterojunction photocatalysts with excellent photocatalytic performances

A novel 2D/3D Z-scheme g-C₃N₄/SnS₂ photocatalyst was successfully fabricated via self-assembly forming 3D flower-like SnS₂ microspheres on the surface of the 2D g-C₃N₄ nanosheets. The photocatalytic performances of the samples were systematically explored through catalytic reduction of Cr⁶⁺ and oxidation of Bisphenol S (BPS) under the illumination of visible light, and the photocatalytic degradation pathway of BPS was also proposed based on the degradation products confirmed by GCMS. Among the as-prepared samples, 0.4-g-C₃N₄/SnS₂ exhibited the most efficient photocatalytic performances, and the apparent quantum efficiency (QE) for the removal of Cr⁶⁺ could achieve 30.3 %, which is 2.8 times higher than that of the SnS₂. The enhancing photocatalytic activities originated from the efficient interfacial charge migration and separation obtained in g-C₃N₄/SnS₂, which was firstly verified via the photoluminescence spectra, time-resolved photoluminescence spectra and photoelectrochemical characterizations. Importantly, the DFT calculated shows that the band distribution of the g-C₃N₄/SnS₂ sample is staggered near the forbidden, which can facilitate the efficient interfacial charge migration and separation as well as result in the improvement of the catalytic activity. Finally, we put forward a more reasonable Z-scheme charge transfer mechanism, it was verified by analysing the results of free radical scavenging tests, EPR experiments and theoretical calculations.

Carbothermal synthesis of biochar-supported metallic silver for enhanced photocatalytic removal of methylene blue and antimicrobial efficacy

Pinewood biochar (PBC)-supported metallic silver (Ag^o) was prepared via a one-step carbothermal reduction route (AgH) or a wet-chemistry reduction method (AgW). XRD and SEM confirmed Ag^o was soldered on PBC matrix. Low methylene blue (MB) sorption was observed for unsupported Ag^o nanoparticles (AgNP), AgH and AgW. Under ultraviolet (UV) light irradiation, net MB degradation by AgH (15.88 g kg^-1) was higher than that of AgW (12.50 g kg^-1) and AgNP (10.27 g kg^-1). TOC removal percentages after degradation corresponded largely to reduction of MB concentrations in solution, indicating MB was dominantly mineralized. Electron paramagnetic resonance (EPR) revealed that MB was degraded by reactive oxygen species (ROS) such as hydroxyl radical (OH), superoxide radical (O₂-) and singlet oxygen (¹O₂). The scavenging experiments further suggested that OH scavengers suppressed MB degradation to a greater extent than other quenchers. Compared to AgW, AgH possessed greater abundance of persistent free radicals, which enhance ROS generation. PBC could also improve separation of electron-hole (e^--h⁺) pairs and enhance electron transfer ascribing to favorable carbon structure. Besides, PBC-Ag^o maintained good antimicrobial efficacy over E.coli DH5α. This work presented a facile carbothermal route to prepare Ag^o-based photocatalysts for dye removal and microbial inhibition in industrial wastewater.

Doping of Graphitic Carbon Nitride with Non-Metal Elements and Its Applications in Photocatalysis

This review outlines the latest research into the design of graphitic carbon nitride (g-C3N4) with non-metal elements. The emphasis is put on modulation of composition and morphology of g-C3N4 doped with oxygen, sulfur, phosphor, nitrogen, carbon as well as nitrogen and carbon vacancies. Typically, the various methods of non-metal elements introducing in g-C3N4 have been explored to simultaneously tune the textural and electronic properties of g-C3N4 for improving its response to the entire visible light range, facilitating a charge separation, and prolonging a charge carrier lifetime. The application fields of such doped graphitic carbon nitride are summarized into three categories: CO2 reduction, H2-evolution, and organic contaminants degradation. This review shows some main directions and affords to design the g-C3N4 doping with non-metal elements for real photocatalytic applications.

Using wood flour waste to produce biochar as the support to enhance the visible-light photocatalytic performance of BiOBr for organic and inorganic contaminants removal

In the present study, industrial wood flour waste was selected for the first time as the precursor to produce biochar (WFB). The WFB was then used to prepare WFB/BiOBr visible-light photocatalysts, in which WFB acted as the carbon support to enhance the photocatalytic performance of BiOBr. Specifically, the impact of WFB pyrolysis temperature on the visible-light photo-removal performance of WFB/BiOBr was studied through degrading rhodamine B and reducing Cr(VI). The results indicated that when the pyrolysis temperature was 600 °C, the prepared WFB (600-WFB) had the highest graphitization degree, which afterwards significantly enhanced the visible-light photocatalysis performance of the BiOBr. Having higher graphitization degree, 600-WFB/BiOBr exhibited the highest photocatalytic capability. With a dosage of 0.5 g/L, the 600-WFB/BiOBr could completely remove to 20 mg/L of RhB and 5 mg/L of Cr(VI) within 90 min. Since wood flour is an abundantly existed industrial bioresource waste and easily pyrolyzed to prepare biochar, WFB is a promising alternative to replace traditional carbonaceous materials for the design of green and high-efficient visible-light photocatalysts for environmental remediation.

Development of highly efficient chemosensors for Cu2+ and N2H4 detection based on 2D polyaniline derivatives by template-free chemical polymerization method

Chemosensors play an important role in environmental protection, medical diagnosis and energy conservation. Although polyaniline and its derivatives and two-dimensional (2D) materials have been applied as chemosensors in many reports, the concept of two-dimensional (2D) polyaniline derivatives has not been achieved in chemosensors. Here, two kinds of two-dimensional (2D) polyaniline derivatives are designed and synthesized by template-free chemical polymerization. It can be found that these two two-dimensional (2D) chemosensors exhibit high selectivity and sensitivity to Cu²⁺ and N₂H₄. Moreover, it is noteworthy that one of the two-dimensional materials can achieve the limit of detection (LOD) of 45 nM and 8 nM for Cu²⁺ and N₂H₄, respectively. Especially, these results imply that this two-dimensional polyaniline derivative is promising as the chemosensor in sensing field.

Recent Progress in Biochar-Based Photocatalysts for Wastewater Treatment: Synthesis, Mechanisms, and Applications

Biochar (BC) is a carbon-rich material produced from pyrolysis of biomass. In addition to its low toxicity, environmental compatibility, and low cost, BC has the desired advantages of well-developed mesoporous structure and abundant surface functional groups. In recent years, BC-based photocatalysts (BCPs) have played a significant role in many environmental fields. In this paper, we highlight the current progress and several exciting results of BCPs by focusing on their synthesis, characterization, mechanisms, and applications in wastewater treatment. Details on various preparation methods include sol–gel, hydrothermal/solvothermal, ultrasound, calcination, and in situ methods are summarized and discussed. The underlying mechanisms and the applications of BCPs for different semiconductors are reviewed. Furthermore, some future trends and potentials are outlined.