Efficient degradation of VOCs using semi-coke activated carbon loaded ternary Z-scheme heterojunction photocatalyst BiVO4-BiPO4-g-C3N4 under visible light irradiation

The coal chemical industry generates large amounts of solid waste and volatile organic compounds (VOCs). In this study, the solid waste semi-coke powder obtained in the semi-coke production process was used as a raw material to prepare high-specific surface area semi-coke activated carbon (SAC) by a carbonization and activation process, and a ternary z-scheme heterojunction photocatalyst with high catalytic performance was loaded for synergistic treatment by adsorption and photodegradation to achieve waste treatment with waste. The prepared semi-coke activated carbon has a specific surface area of 619.27 m² g^-1, which can achieve effective adsorption of VOCs. The ternary z-scheme heterojunction photocatalyst BiPO₄-BiVO₄-g-C₃N₄ (PVCN) was supported on a semi-coke activated carbon substrate by a one-step sol-gel method. Based on the synergistic effect of adsorption and photocatalysis, the obtained PVCN/SAC material can degrade toluene by 85.6% within 130 minutes under simulated sunlight irradiation, which is 2.43 times that of pure photocatalyst. The rate of degrading toluene can be increased by 4.43 times. Capture experiments showed that superoxide radicals (_˙O₂^-) and hydroxyl radicals (_˙OH) were the key active species in the degradation pathway. Even after five cycles, the material maintained 81.6% of the degradation performance. In this work, we deeply investigate the mechanism of semi-coke activated carbon as a matrix for enhancing photocatalytic degradation performance. The findings of this work provide new insights into the efficient degradation of VOCs and provide a good theoretical basis for the development of high-performance photocatalysts.

Visible-Light-Driven Antimicrobial Activity and Mechanism of Polydopamine-Reduced Graphene Oxide/BiVO4 Composite

In this study, a photocatalytic antibacterial composite of polydopamine-reduced graphene oxide (PDA-rGO)/BiVO4 is prepared by a hydrothermal self-polymerization reduction method. Its morphology and physicochemical properties are characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared (FT-IR), and X-ray diffraction (XRD). The results indicate that BiVO4 particles are evenly distributed on the rGO surface. Escherichia coli (E. coli) MG1655 is selected as the model bacteria, and its antibacterial performance is tested by flat colony counting and the MTT method under light irradiation. PDA-rGO/BiVO4 inhibits the growth of E. coli under both light and dark conditions, and light significantly enhances the bacteriostasis of PDA-rGO/BiVO4. A combination of BiVO4 with PDA-rGO is confirmed by the above characterization methods as improving the photothermal performance under visible light irradiation. The composite possesses enhanced photocatalytic antibacterial activity. Additionally, the photocatalytic antibacterial mechanism is investigated via the morphology changes in the SEM images of MG1655 bacteria, 2′,7′-dichlorofluorescein diacetate (DCFH-DA), the fluorescence detection of the reactive oxygen species (ROS), and gene expression. These results show that PDA-rGO/BiVO4 can produce more ROS and lead to bacterial death. Subsequently, the q-PCR results show that the transmembrane transport of bacteria is blocked and the respiratory chain is inhibited. This study may provide an important strategy for expanding the application of BiVO4 in biomedicine and studying the photocatalytic antibacterial mechanism.

An overview on non-spherical semiconductors for heterogeneous photocatalytic degradation of organic water contaminants

Because of their carcinogenicity and mutagenicity, the elimination of organic contaminants from surface and subsurface water is a subject of environmental significance. Conventional water decontamination approaches such as membrane separation, ultrafiltration, adsorption, reverse osmosis, coagulation, etc., have relatively higher operating costs and can generate highly toxic secondary contaminants. On the other hand, heterogeneous photocatalysis, an advanced oxidation process (AOP), is considered a clean and cost-effective process for organic pollutants degradation. Owing to their distinctive structure and physicochemical properties non-spherical semiconductors have gained considerable limelight in the photocatalytic degradation of organic contaminants. The current review briefly introduces a wide range of organic water contaminants. Recent advances in non-spherical semiconductor assembly and their photocatalytic degradation applications are highlighted. The underlying mechanism, fundamentals of photocatalytic reactions, and the factors affecting the degradation performance are also alluded including the current challenges and future research perspectives.

S-scheme bismuth vanadate and carbon nitride integrating with dual-functional bismuth nanoparticles toward co-efficiently removal formaldehyde under full spectrum light

It is crucial to develop more effective photocatalysts in the field of clean environment. In response, the S-scheme BiVO₄/g-C₃N₄ heterojunction modified by in situ reduced non-noble metal Bi nanoparticles was used to synergistically degrade formaldehyde under full spectral irradiation. The results, that investigated by careful characterizations and density functional theory (DFT) calculations, proved that BiVO₄/g-C₃N₄ form an S-scheme heterojunction, which can effectively improve the separation efficiency of photogenic carriers and maintain the original strong redox capability of semiconductor materials. The SPR effect of Bi elemental substance enhanced the optical response and provided more oxidative species. Thus, the photocatalytic activity of BiVO₄/Bi/g-C₃N₄ was significantly improved through their joint efforts, that the degradation efficiency of HCHO (800 ppm) for 6 h is 96.39% under 300 W Xenon lamp without filter with the pseudo-second-order rate constant of 4.16 ppm^-1·h^-1 and CO₂ selectivity of 98.41%. Surprisingly, the degradation efficiency also reached to 49.35% and 32.23% under visible and near-infrared light irradiation, respectively. Moreover, we also tested its photocatalytic decomposition effect on formaldehyde in coatings, indicating that it has a broad prospect in future coatings applications. This study may provide an expected photocatalyst, an efficient non-noble metal modified S-scheme heterojunction, to degrade volatile organic gases under a broad spectrum light.

In situ ultrasound-assisted ion exchange synthesis of sphere-like AgClxBr1-x composites with enhanced photocatalytic activity and stability

AgCl_xBr_1-x composites with different halogen molar ratios (Cl/Br) were prepared by a facile ultrasound-assisted ion-exchange method. The formation of close contact between AgCl and AgBr facilitated the transportation of photoexcited charge carriers and contributed to the enhanced visible-light-driven photocatalytic degradation of different kinds of antibiotics. The AgCl_xBr_1-x composites had a sphere-like morphology and tunable band gaps from 2.95 to 2.57 eV depending on Cl/Br mole ratios. Besides, the AgCl_xBr_1-x composite was optimized by varying halogen mole ratios (Cl/Br) to achieve the highest photocatalytic activity. Results indicated that AgCl_0.75Br_0.25 showed the best photocatalytic degradation performance, which was about 2.36 and 2.78 times that of the single AgCl towards ciprofloxacin (CIP) and metronidazole (MNZ) degradation, respectively. Meanwhile, a possible photocatalytic degradation mechanism was discussed, and results indicated that the holes (h⁺) and •OH were the dominant active species in the AgCl_0.75Br_0.25 system.

Hydrothermal synthesis of cotton-based BiVO4/Ag composite for photocatalytic degradation of C.I. Reactive Black 5

Photocatalytic materials with high efficiency and convenient recyclability have attracted great interest for the treatment of printing and dyeing wastewater. In this paper, a narrow band gap BiVO₄ photocatalyst was loaded onto Ag modified cotton fabric by a hydrothermal method. The prepared composite materials were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and ultraviolet visible light absorption spectroscopy (UV-vis). The composite materials as prepared show superb photocatalytic activity and reusable performance for the degradation of C.I. Reactive Black 5 (RB5). The degradation rate can reach 99% within 90 min under 1 kW xenon lamp irradiation, and over 90% of the photocatalytic performance is preserved even after five recycles. Furthermore, the photocatalytic mechanism was proposed by spectral analysis and free radical trapping experiments.

Carbon dots sensitized 2D-2D heterojunction of BiVO4/Bi3TaO7 for visible light photocatalytic removal towards the broad-spectrum antibiotics

Focused on the removal of the complicated residual antibiotic in aqueous environment, in this work, a novel carbon dots (C-dots) sensitized 2D-2D heterojunction of BiVO₄/Bi₃TaO₇ were assembled through a simple hydrothermal process. The characteristic by TEM, SEM, and XPS confirmed C-dots evenly anchored on the surface of BiVO₄/Bi₃TaO₇ heterojunction. The as-prepared C-dots/BiVO₄/Bi₃TaO₇ showed superior performance for the degradation of the various antibiotics under visible light illumination. When the concentration of C-dots in the composite is 3 wt.%, the photodegraded rates are obtained to be 91.7%, 89.3%, 87.1%, for tetracycline (TC), amoxicillin (AMX) and ciprofloxacin (CIP), respectively, without significant deactivation during consecutive ten recycle experiments. Furthermore, by assessing the antibiotics mixture solution of TC, AMX and CIP, it is proposed that the prepared samples are potentially effective for the wastewater effluents. A probable mechanism was reasonably proposed. The improved photocatalytic activities could be attributed to the unique construction of the C-dots mediated heterojunction, which could expedite electron migration, improve light harvesting capacity and enhance charge separation efficiency. The present investigation may provide a new perspective to design C-dots mediated heterojunction which could be a potential visible-light-driven photocatalysts for the better practical applications in remediation of broad-spectrum antibiotic residues.

Fabrication of nanostructured NiO/WO3with graphitic carbon nitride for visible light driven photocatalytic hydroxylation of benzene and metronidazole degradation

Fabrication of a novel NiO/WO₃nanohybrid modified graphitic carbon nitride nanosheets with enhanced photocatalytic activity towards photocatalytic hydroxylation of benzene and degradation of a pharmaceutical waste metronidazole.

Visible-light-induced photo-Fenton process for the facile degradation of metronidazole by Fe/Si codoped TiO2

This work investigated the feasibility and efficiency of a heterogeneous photo-Fenton catalyst, Fe/Si codoped TiO₂, for the degradation of metronidazole (MNZ) under visible light irradiation. The Fe/Si codoped TiO₂ was prepared via a facile and simple sol–gel solvothermal process followed by annealing at 480 °C for 4 hours. High resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) measurements revealed that the photo-Fenton process did not change the structure, textural and surface morphologies of this catalyst. Elemental mapping results indicated the good dispersion of Fe and Si ions in TiO₂. Nitrogen adsorption and desorption measurements indicated that Si doping increased the surface area of the catalysts. The Fe and Si doping narrowed the band gap of TiO₂. They also facilitated the transfer of photo-generated electrons from TiO₂ to Fe(iii). Under visible light irradiation and the optimum operating conditions, MNZ could be completely degraded in 50 min by this catalyst within a wide pH range. Hydroxyl radicals and holes were verified to be responsible for degrading MNZ. The leaching of iron ions was less than 0.047 ppm even after illuminating the catalyst for 6 hours, indicating the good stability of the Fe/Si codoped TiO₂. The as-prepared catalysts with excellent catalytic activity, and remarkable reusability and stability could provide a new insight into the preparation of photocatalysts and have wide applications for antibiotics removal.

This work investigated the feasibility and efficiency of a heterogeneous photo-Fenton catalyst, Fe/Si codoped TiO₂, for the degradation of metronidazole (MNZ) under visible light irradiation.