Toxic Organic Pollutants Research Articles

Efficient visible light catalytic degradation of toxic organic pollution by hollow urchin-like TiO2@g-C3N4/GQDs composite

In order to expand the photoresponsive spectrum of TiO2 and improve its catalytic activity under visible light, the hollow urchin-like composites of TiO2@g-C3N4/GQDs (TCN/GQDs) with a core-shell structure heterojunction was synthesized through a hydrothermal method and calcination. Potassium titanium oxalate, melamine, and citric acid were utilized as the raw materials for this synthesis process. The TCN/GQDs composites were subjected to a range of analyses to examine their microstructure and photoelectric properties. The findings indicated that the synthesized composites effectively enhanced the absorption spectrum of TiO2 in the visible light range by creating the stable heterojunctions among TiO2, g-C3N4 and GQDs. Additionally, the ability of these composites to degrade toxic organic pollutants under visible light was studied by using several different organic dyes and antibiotics. The results demonstrated that the TCN/GQDs composites exhibited efficient visible light catalytic degradation capability on organic pollutants, and the degradation efficiency could approach to 100 % under visible light in a short time. Furthermore, the photocatalyst exhibited hardly change of degradation efficiency towards organic pollutants even after 5 cycles of testing, suggesting its commendable performance in visible light catalysis and potential for repeated utilization.

Effect of surfactants (cetyl trimethyl ammonium-bromide, ethyl di-tetra amine and polyacrylamide) on the synthesis of zinc oxide for photocatalytic application

In this work, we report the effect of cetyl trimethyl ammonium bromide (CTAB), ethyl di-tetra amine (EDTA) and polyacrylamide as surfactants on synthesis of zinc oxide for photocatalytic application. The ZnO nanoparticles were synthesized with and without the surfactants and characterized using powder X-ray diffraction (PXRD), and Fourier transform infrared spectroscopy (FTIR). In addition to this, the morphology of zinc oxide prepared in the absence and presence of these surfactants investigated through scanning electron microscopy (SEM). As confirmed from XRD and FTIR characterization results, the use of different surfactants did not affect the composition of ZnO nanomaterials. The photocatalytic activities were investigated by the degradation of methylene blue (MB) dye under sunlight irradiation. To optimize the effects of operational parameters, the study was carried out as a function of dye concentration, catalyst dose, and pH on the degradation efficiency of the photocatalysts. The optimum values of catalyst dose, dye concentration and pH of solution were found to be 0.09 g, 5 mg/L and 10, respectively. The ZnO nanomaterials prepared with CTAB surfactant showed highest degradation efficiency of 98% indicating potential application for practical decontamination of wastewater from toxic organic pollutants. KEY WORDS: Surfactants, Zinc oxide nanoparticles, Photocatalysis, Methylene blue Bull. Chem. Soc. Ethiop. 2024, 38(4), 923-935. DOI: https://dx.doi.org/10.4314/bcse.v38i4.9

Effect of oxidative stress induced by 2,3,7,8- tetrachlorodibenzo-p-dioxin on DNA damage

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly toxic persistent organic pollutant (POP) that can induce DNA damage within cells. Although oxidative stress is one of the primary mechanisms causing DNA damage, its role in the process of TCDD-induced DNA damage remains unclear. In this study, the TCDD-induced production of reactive oxygen species (ROS) and the occurrence of DNA damage at the AP site were monitored simultaneously. Further investigation revealed that TCDD impaired the activities of superoxide dismutase (SOD) and catalase (CAT), compromising the cellular antioxidant defense system. Consequently, this led to an increase in the production of O2.− and NO, thus inducing DNA damage at the AP site under oxidative stress. Our findings were further substantiated by the upregulation of key genes in the base excision repair (BER) pathway and the absence of DNA AP site damage after inhibiting O2.− and NO. In addition, transcriptome sequencing revealed that TCDD induces DNA damage by upregulating genes associated with oxidative stress in the mitogen-activated protein kinase (MAPK), cyclic adenosine monophosphate (cAMP), and breast cancer pathways. This study provides important insights into the toxicity mechanisms of TCDD.

Fungal biomineralization of toxic metals accelerates organic pollutant removal

Fungal biomineralization plays an important role in the biogeochemical cycling of metals in the environment and has been extensively explored for bioremediation and element biorecovery. However, the cellular and metabolic responses of fungi in the presence of toxic metals during biomineralization and their impact on organic matter transformations are unclear. This is an important question because co-contamination by toxic metals and organic pollutants is a common phenomenon in the natural environment. In this research, the biomineralization process and oxidative stress response of the geoactive soil fungus Aspergillus niger were investigated in the presence of toxic metals (Co, Cu, Mn, and Fe) and the azo dye orange II (AO II). We have found that the co-existence of toxic metals and AO II not only enhanced the fungal biomineralization of toxic metals but also accelerated the removal of AO II. We hypothesize that the fungus and in situ mycogenic biominerals (toxic metal oxalates) constituted a quasi-bioreactor, where the biominerals removed organic pollutants by catalyzing reactive oxygen species (ROS) generation resulting from oxidative stress. We have therefore demonstrated that a fungal/biomineral system can successfully achieve the goal of toxic metal immobilization and organic pollutant decomposition. Such findings inform the potential development of fungal-biomineral hybrid systems for mixed pollutant bioremediation as well as provide further understanding of fungal organic-inorganic pollutant transformations in the environment and their importance in biogeochemical cycles.

Major facilitator superfamily transporter PhaT modulates the efflux and degradation of polycyclic aromatic hydrocarbons in Novosphingobium pentaromativorans US6-1

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent and toxic organic pollutants that are widely distributed in nature. Although catabolic pathways are essential for bacteria to effectively utilize PAHs, transporting PAHs and their intermediate metabolites across the bacterial cell envelope is a key factor in PAH catabolism and bacterial survival. In this study, we identified a major facilitator superfamily (MFS) transporter member, PhaT, in a PAH-degrading plasmid of Novosphingobium pentaromativorans US6–1. Evolutionary analyses indicate that PhaT analogs are widely distributed in PAH-degrading bacteria, including the genera Novosphingobium and Sphingobium. Interestingly, deletion of the phaT gene upregulated the levels of PAH-degrading enzymes and PAH-degrading gene expression, thereby accelerating phenanthrene biodegradation. Further studies demonstrated that a deficiency of PhaT impaired the efflux of phenanthrene and its benzene ring-containing intermediate metabolites. Furthermore, the deficiency of PhaT also promoted the biodegradation of naphthalene but not of benzo[a]pyrene. Molecular docking and site-directed mutagenesis revealed the essential roles of hydrophobic amino acids in the PhaT central cavity for binding to benzene ring-containing substrates. Collectively, these findings indicate that PhaT plays a pivotal role in facilitating the efflux of PAHs and their benzene ring-containing intermediate metabolites.

Ag Nanoparticles@Au Nanograting Array as a 3D Flexible and Effective Surface-Enhanced Raman Scattering Substrate.

Surface-enhanced Raman scattering (SERS) is a powerful analytical technique for chemical identification, but it remains a great challenge to realize the large-scale and well-controlled fabrication of sensitive and repeatable SERS substrates. Here, we report a facile strategy to fabricate centimeter-sized periodic Au nanograting (Au-NG) decorated with well-arranged Ag nanoparticles (Ag-NPs) (denoted as Ag-NPs@Au-NG) as a three-dimensional (3D) flexible hybrid SERS substrate with high sensitivity and good reproducibility. The Au-NG patterns with periodic ridges and grooves are fabricated through nanoimprint lithography by employing a low-cost digital versatile disc (DVD) as a master mold, and the Ag-NPs are assembled by a well-controlled interface self-assembly method without any coupling agents. Multiple coupling electromagnetic field effects are created at the nanogaps between the Ag-NPs and Au-NG patterns, leading to high-density and uniform hot spots throughout the substrate. As a result, the Ag-NPs@Au-NG arrays demonstrate an ultrahigh SERS sensitivity as low as 10-13 M for rhodamine 6G with a high average enhancement factor (EF) of 1.85 × 108 and good signal reproducibility. For practical applications, toxic organic pollutants including crystal violet, thiram, and melamine have been successfully detected with high sensitivity at a low detection limit, showing a good perspective in the rapid detection of toxic organic pollutants.

A novel remediation strategy of mixed calcium peroxide and degrading bacteria for polycyclic aromatic hydrocarbon contaminated water

Polycyclic aromatic hydrocarbons (PAHs) are a class of toxic organic pollutants commonly detected in the aqueous phase. Traditional biodegradation is inefficient and advanced oxidation technologies are expensive. In the current study, a novel strategy was developed using calcium peroxide (CP) and PAH-degrading bacteria (PDB) to effectively augment PAH degradation by 28.62–59.22%. The PDB consisted of the genera Acinetobacter, Stenotrophomonas, and Comamonas. Applying the response surface model (RSM), the most appropriate parameters were identified, and the predictive degradation rates of phenanthrene (Phe), pyrene (Pyr), and ΣPAHs were 98%, 76%, and 84%, respectively. The constructed mixed system could reduce 90% of Phe and more than 60% of ΣPAHs and will perform better at pH 5–7 and lower salinity. Because PAHs tend to bind to dissolved organic matter (DOM) with larger molecular weights, humic acid (HA) had a larger negative effect on the PAH-degradation efficiency of the CP-PDB mixed system than fulvic acid (FA). The proposed PAH-degradation pathways in the mixed system were based on the detection of intermediates at different times. The investigation constructed and optimized a novel environmental PAH-degradation strategy. The synergistic application of PDB and oxidation was extended for organic contaminant degradation in aqueous environments.

Interfacial charge transfer in coal gangue/NiO-x composites photocatalyst for efficient-degradation of ciprofloxacin

Coal gangue (CG) is a kind of widespread industrial waste, its large accumulation brings great challenges to the environment. Thus researchers has been widely concerned the efficient utilization of CG. At the same time, fluoroquinolone antibiotics contaminants, such as ciprofloxacin (CIP), are difficult to degrade, have low environmental capacity and wide migration range, and have constantly detected in various kinds of water bodies, and are a kind of toxic organic pollutant. In this study, the CG/NiO-3 composite catalyst was synthesized by chemical precipitation combined with high temperature pyrolysis. Under the conditions of 20.0 mg L−1 CIP concentration, 0.4 g L−1 catalyst dosage and initial pH = 7.0, 180 min of sunlight was simulated, and the removal efficiency reached 87.48%. Through scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption, electron paramagnetic resonance (EPR), found that the degradation efficiency of CG/NiO-3 composites catalyst is improved because the hydroxyl group on the surface of CG promotes the generation of free radicals through the adsorption of oxygen and the introduction of CG increases the specific surface area. It provides more active sites while promoting the interfacial charge transfer and increasing the absorption of sunlight. Therefore, this work provides reference significance and theoretical basis for the resource utilization of CG and the treatment of organic pollutants.

A novel, low-cost, and efficient separation strategy based on S-doped C3N4 for the analysis of PCDD/Fs and dioxin-like PCBs

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) are widespread and highly toxic persistent organic pollutants with similar chemical structure. The popular process for the separation of PCDD/Fs and dl-PCBs in one sample often relies on imported and expensive activated carbon, giving rise to an urgent need of inexpensive and efficient separation method. Herein, a novel, simple, and low-cost separation strategy based on sulfur-doped carbon nitride (S-C3N4) is reported. The S-C3N4 material was synthesized through simple thermal annealing with precursor of thiocyanuric acid. After recovery experiments, the optimal addition ratio of S-C3N4 was determined to be 40% mixed with silica gel. The recoveries for PCDD/Fs and dl-PCBs congeners are 32% - 105% and 60% - 70% respectively, which not only meets USEPA and Chinese standards but also shows comparable performance to activated carbon. Moreover, the proposed S-C3N4 strategy exhibits excellent performance for the analysis of PCDD/Fs and dl-PCBs in real complex samples (sediment and fish liver) in terms of detected concentrations and toxic equivalents. Overall, this study puts forward a new and low-cost avenue for the separation of PCDD/Fs and dl-PCBs, which is of remarkable meaning for motivating the development of detection techniques and domestic equipment for dioxins and other pollutants in the environment.

Green synthesis of lichenan-decorated silver nanoparticles for catalytic hydrogenation of organic dyes and bacterial disinfection

Developing an eco-friendly and efficient homogeneous catalyst for treating complex wastewater containing toxic organic pollutants and bacteria is in significant demand. Herein, ultra-small Ag nanoparticles (NPs)-loaded random coil lichenan nanocomposite (L-AgNP) was prepared through a low-cost and green one-step in-situ reduction strategy using lichenan as the reducing agent. The random coil of lichenan acted as a micro-reactor to disperse and stabilize AgNPs via the Ag-O bonding interaction. In the participation of NaBH4, L-AgNP nanocomposite could achieve greater catalytic efficiency for catalyzing reduction of 4-nitrophenol (∼120 s, 34.34 × 10−3 s−1) with the smaller size of AgNPs or the higher content of Ag. The nanocatalyst also exhibited outstanding catalytic efficiency for congo red, rhodamine B, methylene blue, and methyl orange. The L-AgNP could be easily recycled through ethanol precipitation and continuously reused for ten cycles with a tiny loss of conversion rate. Furthermore, L-AgNP also displayed favorable antibacterial activity, inhibiting the growth of Escherichia coli and Staphylococcus aureus with more than 98 % disinfection ratio. This work provides a green strategy to develop polysaccharide-based multifunctional homogeneous catalysts focusing on wastewater purification.

Salinity-mediated enhancement of quaternary ammonium compounds resistance and removal in endophytic bacteria LSE01

The widespread usage of quaternary ammonium compounds (QACs) as disinfectants during the COVID-19 pandemic poses significant environmental risks, such as toxicity to organisms and the emergence of superbugs. In this study, different inorganic salts (NaCl, KCl, CaCl2, MgCl2) were used to induce endophytes LSE01 isolated from hyperaccumulating plants. After five generations of cultivation under 80 g/L NaCl, the minimum inhibitory concentration (MIC) of LSE01 to QACs increased by about 3-fold, while its degradation extent increased from 8% to 84% for C12BDMA-Cl and 5%–89% for C14BDMA-Cl. Transmission electron microscopy (TEM) and three-dimensional fluorescence spectra indicated that the cells induced by high concentration of salt caused plasmolysis and secreted more bound extracellular polymeric substances (B-EPS); these changes are likely to be an important reason for the observed increased resistance and enhanced degradation extent of LSE01 to QACs. Our findings suggest that salt-induction could be an effective way to enhance the resistance and removal of toxic organic pollutants by functional microorganisms.

Synergism between polyethyleneimine, graphene oxide, and MgFeAl-layered triple hydroxide in removing acid red 1 dye and bisphenol A from contaminated water samples

Water pollution is rapidly growing, requiring the development of effective treatment processes. In this work, a novel adsorbent (composed of polyethyleneimine, graphene oxide, MgFeAl-layered triple hydroxide, abbreviated as PEI@GO/MgFeAl-LTH) was synthesized, characterized, and applied to remove two hazardous water pollutants (i.e., acid red 1 and bisphenol A). The adsorption performance of the synthesized PEI@GO/MgFeAl-LTH nanocomposite was benchmarked to its parental materials (i.e., GO, PEI@GO, MgFeAl-LTH, and GO/MgFeAl-LTH). The results demonstrated that the adsorption capacity of bisphenol A (BPA) and acid red 1 (AR1) onto the nanocomposite are 352.0 and 155.5 mg/g, respectively, which are higher than their adsorption on GO, PEI@GO, MgFeAl-LTH, and GO/MgFeAl-LTH. The obtained adsorption isotherms and kinetics data were fitted using different models, which showed that Redlich-Peterson isotherm and Avrami kinetics models provide excellent fits for the obtained experimental data; the other models provided mixed results. The zeta potential measurements and the study of the pH effect suggest that the adsorption of BPA and AR1 onto the PEI@GO/MgFeAl-LTH nanocomposite is governed by more than a single mechanism. Furthermore, thermodynamics analysis demonstrated that the adsorption of AR1 and BPA is an exothermic (the respective ∆H values are −27.59 and −11.21 kJ/mol), spontaneous, and physical in nature. With respect to the reusability of this nanocomposite, the results revealed that it is highly stable and easily regenerable using a cheap solvent (i.e., 0.2 M NaOH). Accordingly, this study demonstrates the efficacy and superiority of the synthesized PEI@GO/MgFeAl-LTH nanocomposite in efficiently capturing toxic organic pollutants from aqueous environments.

Aggravated visual toxicity in zebrafish larvae upon co-exposure to titanium dioxide nanoparticles and bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate

The bioavailability and toxicity of organic pollutants in aquatic organisms can be largely affected by the co-existed nanoparticles. However, the impacts of such combined exposure on the visual system remain largely unknown. Here, we systematically investigated the visual toxicity in zebrafish larvae after single or joint exposure to titanium dioxide nanoparticles (n-TiO2) and bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH) at environmentally relevant levels. Molecular dynamics simulations revealed the enhanced transmembrane capability of the complex than the individual, which accounted for the increased bioavailability of both TBPH and n-TiO2 when combined exposure to zebrafish. Transcriptome analysis showed that co-exposure to n-TiO2 and TBPH interfered with molecular pathways related to eye lens structure and sensory perception of zebrafish. Particularly, n-TiO2 or TBPH significantly suppressed the expression of βB1-crystallin and rhodopsin in zebrafish retina and lens, which was further enhanced after co-exposure. Moreover, we detected disorganized retinal histology, stunted lens development and significant visual behavioral changes of zebrafish under co-exposure condition. The overall results suggest that combined exposure to water borne n-TiO2 and TBPH increased their bioavailability, resulted in severer damage to optic nerve development and ultimately abnormal visual behavior patterns, highlighting the higher potential health risks of co-exposure to aquatic vertebrates.

Controlled construction of 2D hierarchical core-shell ZnO/MnO2 nanosheets on Nitinol fiber with enhanced adsorption performance for selective solid-phase microextraction of trace polycyclic aromatic hydrocarbons in water samples

BackgroundPolycyclic aromatic hydrocarbons (PAHs) are an important class of potentially toxic persistent organic pollutants in environmental water. Their concentrations are usually too low to allow for direct determination with analytical instruments, and the preconcentration is required prior to instrumental analysis. Solid phase microextraction (SPME) is considered as a high-performance green sample preparation technique for volatile and non-volatile organic compounds due to its high enrichment factor. In fact, the nature of SPME coatings governs the adsorption performance. Therefore, more efforts have devoted to the controlled construction of novel long-life SPME fibers with enhanced adsorption performance and improved adsorption selectivity. Results2D hierarchical core-shell ZnO/MnO2 nanosheets (NSs) were constructed on a Nitinol (NiTi) fiber substrate by layer-by-layer assembly for enhanced and selective SPME of PAHs. Firstly, hexagonal ZnO NSs were electrodeposited on the NiTi substrate. Subsequently smaller secondary MnO2 NSs were uniformly grown on the surface of ZnO NSs by a facile hydrothermal oxidation process. ZnO NSs were well protected by the chemically stable MnO2 shell, making the coating highly durable and efficient for SPME application. Meanwhile, the ZnO/MnO2 NSs coating demonstrated superior adsorption performance for PAHs. After the optimization of SPME conditions, the proposed SPME-HPLC-UV method exhibited good analytical performance for preconcentrating and determining trace PAHs with wide linear ranges (0.03–200 μg L−1) and low LODs (0.005–0.112 μg L−1) as well as good repeatability (1.4%-6.9%) and fiber-to-fiber reproducibility (5.3%-7.1%). Moreover, the proposed method showed good precision and recovery in the preconcentration and determination of target PAHs in real water samples. SignificanceAs compared with representative commercially available fibers, the NiTi@ZnO/MnO2 NSs fiber showed enhanced adsorption efficiency and improved adsorption selectivity for PAHs. The constructed fiber can be used as an alternative to commercial fibers for the adsorption and preconcentration of target PAHs in the environmental water samples. Moreover, the preparation strategy is expected to provide new insights into the precisely controlled construction of the efficient and stable core-shell bimetallic oxide nanostructures on the superielastic NiTi-based fibers.

A novel V/S co-doped BiOBr catalyst for high-efficiency catalytic reduction of toxic organic and hexavalent chromium pollutants under dark

Organic pollutants in industrial and agricultural wastewater can be dangerous to both human health and the environment. Therefore, it is important to develop methods for continuous catalytic reduction of these pollutants under dark conditions as sunlight has geographical and temporal limitations due to different regions, weather conditions, and Earth's rotation. This could have significant implications for practical wastewater treatment. In this study, we successfully synthesized bimetallic vanadium bismuth oxy-sulfo bromide (labeled as VBiOSBr) catalysts using a simple precipitation method by doping V/S into BiOBr to from (Bi,V)(S,O)Br. The morphology, structure, optical absorption properties, electron-hole recombination rate, and reduction performance of the catalysts were examined in detail. The catalyst displayed a tetragonal phase with an energy band gap and specific surface area of approximately 1.93 eV and 22.1 m2/g, respectively. The 1-VBiOSBr catalyst prepared with n(V): n(Bi): n(KBr): n(C2H5NS) = 1: 1: 1: 1 had the best catalytic activity. Within just 14 min, this catalyst removed 98.7% and 96.96% of 4-NP and Cr6+, respectively. The VBiOSBr catalyst remained stable and efficient even after the seventh run, still achieving a removal rate of 94.7%. The study proposed a possible mechanism for 4-NP and Cr6+ reduction activity. The catalyst's simple manufacturing process and its ability to reduce pollutants under dark conditions make it a promising system for practical application in the continuous removal of organic pollutants. So, the VBiOSBr bimetallic catalyst has great potential as a candidate for wastewater treatment technologies.

Enhanced Photocatalytic Performance of rGO Modulated β‐Ga2O3 for Wastewater Treatment

AbstractRapid urbanization has inevitably raised challenges by indirectly adding industry waste to the environment. This problem becomes even more severe when contamination of consumable water is considered. As a leading sector in semiconductor‐related research to face such challenges, gallium oxide and its derivatives have shown remarkable performance by exhibiting controlled, recyclable photocatalytic activities. This work demonstrates the enhancement of the photocatalytic performance of β‐Ga2O3, which is related to the structural and morphological variation induced by rGO wrapping. Firstly, the Ga2O3 nanostructures are obtained by calcinating gallium oxide hydroxide (GaOOH), which is synthesized via a simple chemical route. On the other hand, rGO wrapped β‐Ga2O3 is synthesized using in‐situ hydrothermal treatment. In addition to traditional characterizations such as X‐ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), high‐resolution transmission electron microscopy (HRTEM), Raman spectroscopy, etc., the photocatalytic performance of both pristine and composite systems is studied by time‐dependent UV–Vis absorption spectrum for the degradation of different organic toxic pollutants. It is observed that the composite sample exhibited a larger effective surface area and enhanced optical absorption in the UV–Vis range as compared to the pristine gallium oxide sample. Under UV light irradiation, the rGO wrapped β‐Ga2O3 nanobars can degrade rhodamine B dye entirely within 25 min and exhibit a higher photodegradation rate of 0.1598 min−1 which became 3.5 times higher as compared to that of pure gallium oxide.

Alteration of biomass toxicity in torrefaction – A XDS-CALUX bioassay study

Torrefaction constitutes one of the promising technologies for the management of waste biomass and the production of high-carbon products for combustion, gasification, adsorption of pollutants or soil treatment. Unfortunately, waste biomass may be contaminated with toxic persistent organic pollutants, such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) and dioxin-like biphenyls (dl-PCB). Literature does not provide consistent measurements on how the low-temperature thermochemical processing, such as torrefaction, affects the toxicity of biomass. This contribution assesses how a torrefaction treatment, conducted at 200 °C, modifies the toxicity due to PCDD/PCDF/dl-PCB in biomass. We deploy the XDS-CALUX biotest on five types of waste biomass (sewage sludge, tree bark, cattle manure, spent coffee ground, common reed), before and after treatment. The content of total dioxin- & biphenyl fraction compounds in the raw biomass, investigated in this study, varies from 0.14 to 3.67 pg BEQ·g−1d.m., and in the torrefied biomass between 0.17 and 6.00 pg BEQ·g−1d.m.; BEQ stands for bioanalytical equivalent. This increase is statistically insignificant at p = 0.05, taking into account all types of examined biomass. This proves that low-temperature torrefaction cannot detoxify biomass, i.e., chars, produced from biomass characterized by elevated concentration of PCDD/PCDF/dl-PCB, will reflect the contamination of the feedstocks. With respect to heavy metals, we conclude that only the content of Cd in biomass, and, to a lesser extent, the abundance of Cu and Fe, modify the toxicity of this material during its thermochemical treatment at low temperature.

Synthesis of selenium and fluorine co-doped graphitic carbon nitride for photodegradation of toxic organic pollutants and hydrogen peroxide photoproduction

Science is developing every day to race against the factual growth of industrial pollution in order to redeem the environment. In this study, modification of graphitic carbon nitride via selenium and fluoride doping was successfully conducted. Specifically, the process of co-calcination was conscripted using organic precursors, whilst the foreign elements were obtained from ammonium fluoride and selenium dioxide. The morphological assessment revealed the treated-graphitic carbon nitride possessed a flaky sheet form with high porosity and great crystalline uniformity. Photochemical investigation showed the co-doping of selenium and fluorine elevated the optical properties, including the decrement of bandgap and diminishing the recombination rate of electrons and holes. With interesting improvement in photocatalytic activity, the material was applied in persistent organic compound degradation and hydrogen peroxide production. The treatment improved the degradation percentage, in which the methylene blue removal achieved 99.96 % while the tetracycline removal reached 86.38 %. Moreover, high compatibility and great reusability over 4 cycles were also recorded. When applying the material for the generation of hydrogen peroxide, the co-doped material performance was observed to reach 3307 μM/g.h. The results concluded the advancement in material modification with great application in various aspects.

Insights into the performance of binary heterojunction photocatalysts for degradation of refractory pollutants.

The uncontrolled discharge of industry- and consumer-derived micropollutants and synthetic contaminants into freshwater bodies represents a severe threat to human health and aquatic ecosystem. Inexpensive and highly efficient wastewater treatment methods are, therefore, urgently required to eliminate such non-biodegradable, recalcitrant, and toxic organic pollutants. In this context, advanced oxidation processes, particularly heterogenous photocatalysis, have received enormous attention over the past few decades. Among the different classes of photocatalysts explored by the scientific community, heterojunction photocatalysts, in general, and binary heterojunction photocatalysts, in particular, have shown tremendous promise, attributed to their many distinct advantages. As such, the present review highlights the application of diverse array of binary heterojunction photocatalysts for eliminating water-borne contaminants. Specifically, a bibliometric analysis has been conducted to identify the ongoing research trend and future prospects of heterojunction photocatalysts. It appears that metal oxide/metal oxide-based heterojunctions have superior thermal and mechanical stability compared to other heterojunction photocatalysts. In contrast, metal oxide/non-metal semiconductor-based heterojunctions are extremely effective in pollutant degradation without significant leaching of metal ions. The review concludes by proposing novel strategic research guidelines in order to make further advances in this rapidly evolving cross-disciplinary field of topical interest.

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.