B and cyano groups co-doped g-C3N4 with multiple defects for photocatalytic nitrogen fixation in ultrapure water without hole scavengers

B atoms and cyano groups co-doped graphite carbon nitride with nitrogen vacancies (VN-BC-CN) was explored via one-step in-situ route. A series of comprehensive experiments confirmed that B atoms and cyano groups had been doped into the framework of graphite carbon nitride, forming VN-BC-CN catalyst sample with a large number of nitrogen-vacancy defects. As electron acceptors, B and cyano groups could be used as active sites for nitrogen conversion. The defect level caused by nitrogen vacancy led to red shift of the light absorption edge, which resulted in higher separation efficiency of photo-induced carriers and faster transfer rate of photo-induced electrons for the VN-BC-CN catalyst. This VN-BC-CN catalyst had good photocatalytic nitrogen fixation performance in the ultrapure water without any hole-scavengers. The nitrogen photofixation rate of VN-BC-CN (115.53 μmol g^-1 h^-1) was 25.5 times that of pure carbon nitride (GCN, 4.53 μmol g^-1 h^-1). Moreover, NH₄⁺ generation rate hardly decreased after 10 h reaction, and the NH₄⁺ generation rate could reach 79.56 μmol g^-1 h^-1 in the fifth cycle, showing the good photocatalytic stability of the VN-BC-CN catalyst.

Novel AgI/BiSbO4 heterojunction for efficient photocatalytic degradation of organic pollutants under visible light: Interfacial electron transfer pathway, DFT calculation and degradation mechanism study

Herein, we constructed a novel AgI/BiSbO₄ heterojunction via a hydrothermal-precipitation method. The heterojunction structure boosts the generation of hydroxyl and superoxide radicals for efficient degradation of organic pollutants. The photocatalytic activities of the optimal sample for ARG and TC degradation are 10 and 1.6 times higher than those of bare AgI, respectively. Characterizations and theoretical calculations together confirm a strong interfacial charge transfer exists between the interlayer in AgI and BiSbO₄ by the formation of Ag‒O bond, making O atoms obtain rich free electrons from Ag atoms of AgI, thus forming an ultrahigh electron transfer tunnel, and ultimately accelerating the separation of photoinduced electrons. More interestingly, low amounts of Ag⁰ NPs formed during the photocatalytic process, enhancing the visible light absorption because of its SPR (surface plasmon resonance) effect and further promoting the separation of photoinduced carriers. Furthermore, photocatalytic degradation pathways were proposed in detail by analyzing intermediates and a reasonable photocatalytic mechanism was unearthed. This work extends the development of AgI-based heterojunction photocatalysts.

Photodegradation mechanisms of reactive blue 19 dye under UV and simulated solar light irradiation

In this work we performed dye photodegradation experiments in presence of TiO₂ and Cu/Zr modified TiO₂. The changes in the shape of the spectra of RB19 caused by photocatalysts under the simulated solar or UV light were monitored. Since the predominant photocatalytic mechanism can only be observed in very dilute solution of RB19, UV-Vis absorption spectrometry for higher concentrations and thermal lens spectrometry for lower concentrations have been applied to elucidate the mechanistic details of degradation processes. Bleaching of the dye was a characteristic feature, that occurred under both simulated solar and UV lights. It was also evident, that the absorption peak with maximum centered at 592 nm undergoes a slight blue shift during irradiation. The experiments carried out using UV and simulated solar light demonstrated, that two different processes responsible for the RB19 dye degradation occurred. In the initial stage of irradiation one of the processes appears under the UV light and can be recognized by a characteristic blue shift in the absorption spectrum of the solution. The second process is characteristic for irradiation by the simulated solar light which involve a blue shift at longer periods (100 min). These phenomena were attributed to the photocatalytic and photosensitization mechanisms, respectively. However, photocatalytic mechanism was also observed under simulated solar radiation, when the initial dye concentration was decreased to 5 mgL^-1, and was recognized by the increase of the thermal lens signal during the initial stages of degradation process. This was possible because the thermal lens spectroscopy technique provides a limit of quantification for RB19 at the concentration level of 0.12 mg L^-1, while UV-Vis spectrometry enables quantification of RB19 only down to 4 mg L^-1 levels.

Livistona jekinsiana fabricated ZnO nanoparticles and their detrimental effect towards anthropogenic organic pollutants and human pathogenic bacteria

An environment-friendly and economically sound method was developed to achieve a multi-functional ZnO nanoparticles (ZnO NPs) using water extract of Livistona jekinsiana. The ZnO NPs absorbed maximum wavelength of light at 332 nm in UV-Visible spectroscopy (UV/Vis). X-Ray Diffraction (XRD) pattern revealed the crystallinity of the nanoparticles with the crystallite size around 22.45 nm. The geometry, shape, size, and elemental composition were determined by Transmission Electron Microscope (TEM) and Energy Dispersive Spectroscopy (EDS). The presence of phytochemicals and the typical zinc-oxygen group in the ZnO NPs was implied by Fourier Transform Infrared spectroscopy (FTIR). Photo luminescence spectroscopy (PL), and Dynamic Light Scattering (DLS) techniques were also used to characterize and study the different features of ZnO NPs. The multifunctional ZnO NPs showed an efficient photodegradative effect towards the degradation of two anthropogenic dyes, methyl orange (MO) and methylene blue (MB) under solar radiation. The degradation reaction of MO and MB was compliantwithzero-order kinetics and first-order kinetics respectively. Also, Livistona jekinsiana fabricated ZnO NPs showed potential Antibacterial activity against S. aureus, B. subtilis, E. coli and K. pneumonia bacteria and effective antioxidant activity using DPPH scavenging assay. The mechanism of the antibacterial activity was established by estimating the ROS generation and percentage of DNA in K. pneumonia cell. The study illustrated the reducing and stabilizing property of the Livistona jekinsiana extract as a novel source and potential photodegradative and therapeutic effects of the ZnO NPs.

Enhanced photocatalytic degradation of glyphosate over 2D CoS/BiOBr heterojunctions under visible light irradiation

Two-dimensional (2D) heterojunction photocatalysts can shorten the carrier transfer pathway. In this study, CoS nanoparticles were deposited on the surface of 2D BiOBr nanosheets to fabricate novel ultrathin and intimate-contact 2D heterojunction photocatalysts by a two-step solvothermal route. Under visible-light (λ > 400 nm) irradiation, the apparent reaction rate constant of glyphosate degradation over 10%CoS/BiOBr reaches 0.0074 min^-1 (74.7% glyphosate was degraded within 3 h), which is about 5.3 times that of pure BiOBr (0.0014 min^-1). The extraordinary photocatalytic performance is attributed to the strong visible-light absorption, the effective charge separation and low charge transfer resistance. The possible photocatalytic reaction process and mechanism over CoS/BiOBr heterojunctions are proposed. Moreover, the 10%CoS/BiOBr sample shows good reusability and stability. This work could provide a new insight for the design and development of 2D heterojunction photocatalysts.

A novel strategy for sequential reduction of nitrate into nitrogen by CO2 anion radical: Experimental study and DFT calculation

In order to expand the application of CO₂ anion radical (CO₂^-), as a novel green reductant in the control of environmental pollution, CO₂^- radical was induced into the reduction of nitrate. The reduction efficiency, products and mechanism of nitrate or nitrite by CO₂^- radical were investigated based on the results of batch experiments and theoretical calculation using density functional theory (DFT) methods, respectively. It was found that: (1) the efficiency of nitrate reduction by CO₂^- radical from the HCOOH/UV system was far lower than that of nitrite under the same reaction conditions, (2) the rate-control step of nitrate reduction by CO₂^- radical was the transformation process of nitrate into nitrite with an activation energy of 23.9 kcal/mol, (3) the final products of nitrate reduction were mainly composed of nitrogen (N₂). On this basis, a novel strategy of rapid reduction of nitrate into N₂ using CO₂^- radical was proposed. Specifically, nitrate was firstly reduced into nitrite with the assistance of Zn/Ag bimetal, and then nitrite was further reduced into N₂ by CO₂^- radical. In this way, the removal efficiency of nitrate was all achieved nearly 100% in the initial nitrate concentration ranging from 25 to 100 mg (N)/L, while the highest N₂ selectivity could reach 97.5%. This work provided a promising approach for the reduction of nitrate into nitrogen with high efficiency and high N₂ selectivity by CO₂^- radical.

Metal organic framework-derived C-doped ZnO/TiO2 nanocomposite catalysts for enhanced photodegradation of Rhodamine B

A series of C-doped ZnO/TiO₂ composites with various molar ratios of ZnO to TiO₂ were synthesized by one-step controllable pyrolysis of Zn/Ti bimetallic metal-organic frameworks (Zn/Ti-MOF). The Zn/Ti-MOF was prepared using a facile microwave hydrothermal method. Electron microscopic analysis proved that the composites presented regularity cubic morphology with an edge length of about 1 μm and the C atoms were successfully doped into ZnO/TiO₂ composites. X-ray photoelectron spectroscopy (XPS) measurement results confirmed the C-doping in the ZnO/TiO_2. Comparative experimental studies showed that 2% ZnO/TiO₂ composites prepared with the calcination temperature of 600℃ displayed the best photocatalytic degradation efficiency (94%) of RhB under the simulated sunlight irradiation. Cyclical experiment indicated the high stability and reusability of 2% ZnO/TiO₂ composites. Electron spin resonance (ESR) and trapping experiments illustrated that the produced O₂^- served as the main active species for the efficient RhB removal. This work provides an efficient way for preparing C-doped bimetal oxides composites, which would have an important application prospect in the photocatalytic degradation of organic pollutants in environmental water.

Defect enrich ultrathin TiO2 nanosheets for rapid adsorption and visible light mediated PPCPs degradation

Recently, PPCPs have attracted extensive attention as emerging pollutants. Due to the strong hydrophilicity and small molecular weight, PPCPs are difficult to be fully removed by adsorption and other processes, posing a serious threat to the ecological environment. Here, we demonstrate solvothermal synthesis of defect enrich TiO₂ nanosheets through simple copper doping. Novel TiO₂ nanosheets were found to be mesoporous with high specific surface area and exhibited excellent visible light response. Performance of the developed TiO₂ nanosheets were evaluated towards photocatalytic degradation of two model pollutants, tetracycline and acetaminophen. Results showed robust degradation of tetracycline and acetaminophen under visible-light irradiation within 100 min. Meanwhile, the potential relationship between the structural characteristics and excellent ability of the catalyst was discussed, as well as probable mechanism. Additionally, a study on the toxicity of tetracycline solution to human skin epidermal cells showed that the toxicity of the treated solution to cells is greatly reduced. The prepared catalysts show good repeatability (a slightly decrease ca.3% after 5 cycles) and applicability, providing a reasonable design for water remediation.

Diversity of experimental designs for the fabrication of antifungal surfaces for the built environment

The fungal infestation in construction industries is a major problem with a very high removal cost that needs to be controlled not only to prevent the fouling of surfaces but also to prevent allergic reactions or respiratory problems especially in immunocompromised individuals. To combat fungal invasion, several experimental approaches to produce antifungal surfaces have been developed. Here, we reviewed the current strategies in designing antifungal surfaces and classified those approaches into two major categories: the chemical and/or physical modification of the actual material surface and nanoparticle-based coating formulations created using the functionalised nanoparticles. KEY POINTS: • Antifungal effect of micro- and nano-structured superhydrophobic surfaces. • Long-term antifungal effect conferred through biocides. • Advanced coatings based on functionalised silica, TiO₂ and ZnO nanoparticles.

Microplastic degradation by hydroxy-rich bismuth oxychloride

Microplastics, as a class of widely dispersed persistent pollutants, the main reactive oxygen species is far from clarified in their photocatalytic degradation. In this study, a novel hydroxy-rich ultrathin BiOCl (BiOCl-X) was prepared at room temperature. BiOCl-X shows a strong potential for photocatalytic degradation of microplastics, and the mass loss of plastics is 24 times higher than that of the BiOCl nanosheets. More importantly, we explored the photocatalytic mechanism through electron paramagnetic resonance and capture experiments, and found that the surface hydroxyl of BiOCl can effectively enhance the production of hydroxyl radicals, resulting in boosting degradation performance. Here, we provide new insights that photocatalytic degradation of microplastic is dependent on surface hydroxyl groups. This work could be useful for controllable designs of hydroxy-rich photocatalysts for applications in microplastic degradation.

A novel PVDF-TiO2@g-C3N4 composite electrospun fiber for efficient photocatalytic degradation of tetracycline under visible light irradiation

A novel composite electrospun fiber with high photocatalytic efficiency, good stability, strong hydrophobicity, good pollution resistance, and easy separation and recovery was synthesized. The TiO₂@g-C₃N₄ (TCN) with special core-shell structure (5-10 nm shell) facilitated the separation of photogenerated electron-holes and had high photocatalytic performance. The poly (vinylidene fluoride) (PVDF) electrospun fiber immobilized with TCN was successfully fabricated (PVDF-TCN) with uniform distribution and size of nanofibers by using electrospinning, which was used for degrading tetracycline under visible-light irradiation (> 400 nm). A special rougher surface of electrospun fiber obtained by washing of sacrificial PVP increased the specific surface area, which became more conducive to the adhesion of the catalyst. The water contact angle and FTIR results demonstrated that the electrospun fiber became extremely hydrophilic after adding TCN catalyst, which could effectively mitigate the fiber pollution. The PVDF-TCN-0.2g electrospun fiber exhibited excellent photocatalytic performance and the degradation efficiency of tetracycline was up to 97% in 300 min under visible-light irradiation. The mechanism of PVDF-TCN electrospun fiber degradation of tetracycline in the photocatalytic process was also proposed. In addition, the PVDF-TCN-0.2g exhibited a stable activity after 4 cycles experiments since the degradation efficiency remained about 90%. Therefore, we believed this study provided a new strategy in catalyst immobilization and wastewater treatment.

In situ synthesis of Ag3PO4/C3N5Z-scheme heterojunctions with enhanced visible-light-responsive photocatalytic performance for antibiotics removal

Environmental pollution caused by antibiotics-containing wastewater has attracted increasing attention. Considering the superior photocatalytic performance and the issue of photo-corrosion over silver-based photocatalysts, it is desirable to construct silver-based photocatalysts with high photostability. Herein, a serious of Ag₃PO₄/C₃N₅ nanocomposites with Z-scheme band alignment were rationally designed and fabricated for tetracycline hydrochloride (TCH) removal. A variety of characterizations were employed to systematically study the phase structure, morphology and microstructure, optical properties, surface chemical states, and photocatalytic performance of the as-fabricated photocatalysts. The as-prepared Ag₃PO₄/C₃N₅ nanocomposites exhibited superior photocatalytic activity and photochemical stability than a single component toward TCH removal, meanwhile, the photocatalytic performance was not increased with the increasing amount of Ag₃PO₄. The possible photocatalytic mechanism (Z-scheme mechanism) was investigated and verified. The Z-scheme heterojunctions formed between Ag₃PO₄ and C₃N₅ is the main reason for the enhanced photocatalytic activities.

Adsorption-photocatalytic processes for removal of pentachlorophenol contaminant using FeNi3/SiO2/ZnO magnetic nanocomposite under simulated solar light irradiation

The adsorption followed by photocatalytic degradation process was examined for the pentachlorophenol (PCP) removal from aqueous solution. These processes were accomplished by using FeNi₃/SiO₂/ZnO magnetic nanocomposite as an adsorbent-photocatalytic agent and under the irradiation of solar light. The magnetic nanocomposite used was first synthesized and then was characterized using transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), vibrating-sample magnetometer (VSM), and X-ray diffraction (XRD) spectroscopy. The PCP removal efficiency was tested for various factors, including pH, PCP concentration, and nanocomposite dose at different contact times. The characterization results of TEM, FE-SEM, and VSM analysis showed that the synthesized nanoparticles are amorphous and tend to agglomerate due to their high super-paramagnetic property. In addition, the EDX technique showed that the Zn and O elements had the highest weight percent in the synthesized nanocomposite, respectively. On the other hand, XRD analysis revealed that the crystalline size of the nanoparticles was about 42 nm. The kinetic of PCP degradation followed the pseudo-first-order model with R² = 0.978. According to the results of the isotherm study, the adsorption of PCP onto the nanoparticles followed the Freundlich model. The results of adsorption-photocatalytic degradation experiments showed that 100% removal of PCP was obtained at optimum conditions of pH = 3, nanocomposite dose = 0.5 g/L, contact time = 180 min, and initial PCP concentration of 10 mg/L. Through the results obtained from this study, the adsorption process followed by solar light photocatalytic degradation process using FeNi₃/SiO₂/ZnO magnetic nanocomposite is found to be an efficacious treatment method for the removal of PCP contaminant from water and wastewater.

Silicate glass matrix@Cu2O/Cu2V2O7 p-n heterojunction for enhanced visible light photo-degradation of sulfamethoxazole: High charge separation and interfacial transfer

Focusing on the treatment of pharmaceuticals contaminated water by advanced oxidation processes, a novel three dimensional silicate glass matrix (3-DG) coupled Cu₂O/Cu₂V₂O₇ p-n heterojunction was constructed by in-situ hydrothermal technique. The optimal Cu₂O/Cu₂V₂O₇ with 30 wt % Cu₂V₂O₇ (CV-30) degrades 90.1 % sulfamethoxazole (SMX) in 60 min and nearly 100 % removal in 45 min via coupling with 3-DG. Under natural sunlight ∼ 80 % SMX removal was observed. The internal electric field of the p-n junction facilitates the electron flow via the interface. 3-D silicate glass increases the visible light absorption dramatically via internal reflection which facilitates higher exposure for the junction and shortens the diffusion length of charge carriers. The effect of reaction parameters suggests that HCO₃^- and CO₃^2- ions substantially escalate the SMX removal rate. Scavenging experiments and ESR probe suggest O₂^- as the main active species followed by OH radicals. The degradation products were detected by LC-MS analysis and a degradation mechanism was also predicted. The photocatalytic mechanism was explained in terms of the electron transfer facilitated by conventional transfer and Z-scheme. This strategy to construct such highly visible and solar active p-n heterojunctions will pave way for future opportunities for the degradation of recalcitrant pharmaceutical pollutants.

Preparation of CuSe-PDA/g-C3N4 and its visible-light photocatalytic performance to dye degradation

CuSe as an excellent photocatalytic semiconductor material has wildly used in the field of photocatalysis. In this paper, CuSe-PDA/g-C₃N₄ was designed and synthesized, and the photocatalytic performance of CuSe was further enhanced by the addition of polydopamine (PDA) and graphite phase carbon nitride (g-C₃N₄). The as-prepared CuSe-PDA/g-C₃N₄ was characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and elemental mapping. The specific surface area and porous characteristics of the material were also studied by N₂ adsorption-desorption isotherm, which the specific surface area were 186.6 m²/g and pore size were of 3.1 nm by BET data analysis. The photocatalytic conditions for the degradation of methylene blue (MB) by CuSe-PDA/g-C₃N₄ were optimized in the experiment. The results showed that the photocatalytic performance of CuSe-PDA/g-C₃N₄ under visible-light illumination were better than CuSe and PDA owing to the narrow band gap energy and delayed electron-hole recombination. Under the optimized conditions, the removal rate reach to 99% of 50 mg/L MB within 60 min irradiation time. Moreover, the MB removal rate was over 90% through six repeated experiments, which proved that the CuSe-PDA/g-C₃N₄ composite nanomaterials have good stability and reusability.

Photodegradation of Pharmaceutical and Personal Care Products (PPCPs) and Antibacterial Activity in Water by Transition Metals

The intensity of emerging pollutants such as pharmaceuticals and personal care products (PPCPs) in the aquatic and terrestrial environment is a major source of concern to researchers. The current conventional methods of wastewater treatment plants are considered not efficient enough in the complete removal of the recalcitrant contaminants from water. The use of modified transition metals in visible responsive synthesis to degrade PPCPs and other pollutants (organic and inorganic) is considered as a developing green chemistry and sustainable technology. Hence, this review presents the state-of-the-art discussion on the novel photodegradation of PPCPs, and antibacterial activities of transition metal-modified magnetite materials for wastewater treatment, and suggested directions for the future. Transition metal-modified magnetite nanostructured photocatalysis is identified as one of the best candidates employed in advanced oxidation processes (AOPs) for wastewater treatment and has been found to efficiently destroy bacterial spores and effectively remove recalcitrant pollutants in water. Therefore, this article hopes to contribute scientific knowledge along with existing ones on advanced mechanisms and technology used in wastewater treatment.

A potent multifunctional Ag/Co-polyvinylpyrrolidone nanocomposite for enhanced detection of Cr(III) from environmental samples and its photocatalytic and antibacterial applications

Trivalent chromium (Cr(III)) is considered to exhibit hormesis (bi-phasic dose-response) property, where low dose be beneficial and high dose shows toxic effect. The present work describe the development of a bimetallic Ag/Co-polyvinylpyrrolidone nanocomposite (Ag/Co-PVP NPs) probe to detect and quantify Cr(III) ions from aqueous samples. The hydrodynamic size and zeta potential of the particle was determined to be 29 ± 1.3 nm and -37.19 ± 2.4 mV respectively. The interaction of Cr(III) with Ag/Co-PVP probe showed drastic change in colour of NPs from dark brown to pale yellow, with corresponding blue shift, tapering width and increased peak intensity. The probe showed high specificity towards Cr(III) among the tested metal ions. A linearity was observed between various dilutions of Cr(III) ions (10 to 50 nM) and the absorbance of Ag/Co-PVP NPs at 428 nm with R² value of 0.998. The minimum detectable limit of Cr(III) was calculated to be 0.6 nM. The influence of salinity, temperature and pH on detection was studied. The probe was found to detect Cr(III) at acidic pH effectively. Competitive metal ions did not interfere the detection of Cr(III). The water sample collected from Noyyal river was taken to estimate Cr(III) by using the prepared probe to ensure practical applicability. The sample contains 9.3 nM of Cr(III) that was cross verified with AAS analysis. Hence, it is understood that the reported probe can be used to detect Cr(III) selectively with high accuracy from aqueous samples. In addition, the particles also exhibited excellent photocatalytic activity under visible light. Ag/Co-PVP nanocomposites exhibited excellent antibacterial activity against both gram +ve (B. subtilis) and gram -ve (E. coli) bacteria.

Degradation of aliphatic halogenated contaminants in water by UVA/Cu-TiO2 and UVA/TiO2 photocatalytic processes: Structure-activity relationship and role of reactive species

This study investigated the degradation of eight aliphatic halogenated contaminants (one brominated flame retardant and seven disinfection by-products) in synthetic drinking water by the UVA/TiO₂ and UVA/Cu-TiO₂ processes. The degradation rate constants of 2,2-bis(bromomethyl)-1,3-propanediol and trichloromethane in the UVA/Cu-TiO₂ process were 10.1 and 1.29 times, respectively, higher than those in the UVA/TiO₂ process. In contrast, the degradation rate constants of dichloroacetaldehyde, monochloroacetonitrile, monobromoacetonitrile and dibromonitromethane in the UVA/Cu-TiO₂ process were 8.15, 2.33, 2.84 and 1.80 times, respectively, lower than those in the UVA/TiO₂ process. The degradation rate constants of monobromonitromethane and dichloronitromethane were comparable in the two processes. The relationships between the degradation rate constants and the structural characteristics of the selected contaminants were examined to explain the different degradation efficacies of the contaminants in the two processes. As suggested by a quantitative structure-activity relationship (QSAR) model, the UVA/TiO₂ process favored the degradation of contaminants with more polar electron-withdrawing moieties and higher degrees of chlorination. While the UVA/Cu-TiO₂ process favored the degradation of hydrophilic unsaturated contaminants with multiple bonds. The concentrations of the reactive species (e.g., HO and e^-) generated in the two photocatalytic processes were quantified using competition kinetics. The UVA/Cu-TiO₂ process generated >10 times higher concentrations of HO than the UVA/TiO₂ process, suggesting that the former process was more suitable for the degradation of contaminants that are reactive towards HO, while e^- and e^--derived superoxide radicals were non-negligible contributors to contaminant degradation in the UVA/TiO₂ process.

Preparation of PVDF/CdS/Bi2WO6/ZnO hybrid membrane with enhanced visible-light photocatalytic activity for degrading nitrite in water

In this work, a visible light-driven ternary heterojunction photocatalyst, CdS/Bi₂WO₆/ZnO, was synthesized using hydrothermal, ultrasonic dispersion, and deposition precipitation methods. The results show that photocatalysts with flower-like heterostructures were obtained, which could efficiently separate electron-hole pairs, and the photocatalytic activity was thereby significantly enhanced. Furthermore, CdS/Bi₂WO₆/ZnO and polyvinylidene fluoride (PVDF) were used to fabricate hybrid membranes via a phase-conversion method. The samples were characterized using SEM, TEM, EDX, XRD, DRS, XPS, PL, and N₂ adsorption-desorption isotherms, and the transient photocurrent response. The photocatalytic activity of the hybrid membrane was evaluated, and 92.58% of the nitrite was converted into non-toxic substances within 4 h under simulated sunlight irradiation. This result indicated that the photocatalyst exhibited a good photocatalytic activity after immobilization. The possible mechanism was elucidated by studying the product during the photocatalytic degradation, and the effects of different pH values, electron scavengers, and hole scavengers on the photocatalytic performance were further investigated.

Preparation of Ag-cellulose nanocomposite for the selective detection and quantification of mercury at nanomolar level and the evaluation of its photocatalytic performance

Mercury is a toxic heavy metal that reaches to the water bodies mainly by coal burning, mining and petrol refining. The study was focused to investigate the application of Ag-cellulose nanocomposite to detect and quantify mercury colorimetrically. The Ag-cellulose nanocomposite was characterized by X-ray diffraction, Transmission electron microscopy, Fourier transform infrared spectroscopy, UV-visible spectroscopy, particle size analyzer and zetasizer. The study identified that the presence of other metal ions did not interfere with the detection of Hg²⁺ ion by the probe. The prepared Ag-cellulose nanocomposite-phenylalanine conjugate incorporated paper strip showed an excellent result in Hg²⁺ detection. The Ag-cellulose nanocomposite was used to quantify the unknown concentration of mercury on real sample (environmental sample) and it was found to be highly accurate by confirming with atomic absorption spectrophotometric analysis. The Ag-cellulose nanocomposite showed effective detection at 45 °C, pH 9 and 0.1% of salinity. The Ag-cellulose nanocomposite showed efficient photocatalytic performance under visible light irradiation. The half-life period of MB by Ag-cellulose nanocomposite under visible light was determined to be 90 min. The study suggests the application of prepared probe in photocatalysis and the detection of Hg²⁺ from various environmental samples.

Ag3PO4 decorated black urchin-like defective TiO2 for rapid and long-term bacteria-killing under visible light

Both phototherapy via photocatalysts and physical puncture by artificial nanostructures are promising substitutes for antibiotics when treating drug-resistant bacterial infectious diseases. However, the photodynamic therapeutic efficacy of photocatalysts is seriously restricted by the rapid recombination of photogenerated electron–hole pairs. Meanwhile, the nanostructures of physical puncture are limited to two-dimensional (2D) platforms, and they cannot be fully used yet. Thus, this research developed a synergistic system of Ag₃PO₄ nanoparticles (NPs), decorated with black urchin-like defective TiO₂ (BU–TiO_2-X/Ag₃PO₄). These NPs had a decreased bandgap compared to BU-TiO_2-X, and BU-TiO_2-X/Ag₃PO₄ (3:1) exhibited the lowest bandgap and the highest separation efficiency for photogenerated electron–hole pairs. After combination with BU-TiO_2-X, the photostability of Ag₃PO₄ improved because the oxygen vacancy of BU-TiO_2-X retards the reduction of Ag⁺ in Ag₃PO₄ into Ag⁰, thus reducing its toxicity. In addition, the nanospikes on the surface of BU-TiO_2-X can, from all directions, physically puncture bacterial cells, thus assisting the hybrid's photodynamic therapeutic effects, alongside the small amount of Ag⁺ released from Ag₃PO₄. This achieves synergy, endowing the hybrid with high antibacterial efficacy of 99.76 ± 0.15% and 99.85 ± 0.09% against Escherichia coli and Staphylococcus aureus, respectively, after light irradiation for 20 min followed by darkness for 12 h. It is anticipated that these findings may bring new insight for developing synergistic treatment strategies against bacterial infectious diseases or pathogenic bacterial polluted environments.

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BU-TiO_2-X/Ag₃PO₄ (3:1) hybrid improved the photostability of Ag₃PO₄.

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BU-TiO_2-X/Ag₃PO₄ (3:1) hybrid exhibited outstanding photodynamic therapeutic effects.

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The nanospikes from all directions on the BU-TiO_2-X physically punctured bacterial cells.

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The physical puncture combined with the Ag⁺ released by Ag₃PO₄ had long-term bacteriostatic efficacy.

Fabricating acid-sensitive controlled PAA@Ag/AgCl/CN photocatalyst with reversible photocatalytic activity transformation

Achieving the intelligent controllability of the photocatalyst to the surrounding environment is a very meaningful work. Here, the polyacrylic acid (PAA) modified Ag/AgCl-40/CN composite was constructed to achieve an intelligent response of pH value. PAA exhibits hydrophilic properties at high pH value, increasing the adsorption capacity to tetracycline (TC) molecules. The morphology of PAA from contracted state to diastolic state, releasing the Ag/AgCl-40/CN catalyst. In addition, PAA modified Ag/AgCl-40/CN can prevent the loss of AgCl. The g-C₃N₄ nanosheets (CN) as a carrier enhance the dispersibility of the AgCl particles. The LSPR effects of Ag nanoparticles produce more electrons acting on photocatalytic degradation. On the results of experiment, the degradation of TC by PAA@Ag/AgCl-40/CN shows an excellent degradation activity when the high pH value. Photoluminescence spectroscopy and photocurrent demonstrate that carrier separation efficiency of PAA@Ag/AgCl-40/CN is higher than CN and Ag/AgCl-40/CN. The detection of the main active substances •O₂^- and h⁺, revealing a reasonable mechanism for the PAA@Ag/AgCl-40/CN hybrid system. This work provides a procedure to obtain smart materials that can switch photocatalytic processes.

In situ growth of carbon nitride on titanium dioxide/hemp stem biochar toward 2D heterostructured photocatalysts for highly photocatalytic activity

In this work, hierarchical structure TiO₂/hemp stem biochar carbon (HSBC) and C₃N₄-TiO₂/HSBC were successfully fabricated, which were used as efficient visible-light photocatalyst degradation for ammonia nitrogen from aqueous solution. The as-prepared C₃N₄-TiO₂/HSBC hybrid catalyst showed the higher efficient photocatalytic activity for decomposition of ammonia nitrogen than those of pure TiO₂ and TiO₂/HSBC, suggesting suppressed recombination of photogenerated charges and promoted mass transfer due to synergistic effect, and thus increased photocatalytic degradation activity. The degradation of ammonia follows a pseudo-first-order kinetics. All prepared catalysts demonstrated extremely photocatalytic efficiency under visible-light and UV light illumination; the ammonia nitrogen photocatalytic degradation activity of C₃N₄-TiO₂/HSBC can reach 90.3% under UV light while the degradation activity achieved about 50.7% under visible-light irradiation. The results revealed that the h⁺ was dominantly active intermediates in the process of photocatalytic degradation. The prepared catalysts are promising for the degradation of ammonia nitrogen from water resource.

Defect-modified reduced graphitic carbon nitride (RCN) enhanced oxidation performance for photocatalytic degradation of diclofenac

Hydroxyl radicals (OH) have robust non-selective oxidizing properties to effectively degrade organic pollutants. However, graphitic carbon nitride (g-C₃N₄) is restricted to directly generate OH due to its intrinsic valence band. In this study, we report a facile environmental-friendly self-modification strategy to synthesize reduced graphitic carbon nitride (RCN), with nitrogen vacancies and CN functional groups. The incorporation of CN enabled to downshift the valence band level, which endowed RCN with the capacity to directly generate OH via h⁺. Experimental and instrumental analyses revealed the critical roles of nitrogen vacancies and CN groups in the modification of the RCN band structure to improve its visible light absorption and oxidizing capacity. With these superior properties, the RCN was significantly enhanced for the photocatalytic degradation of DCF under visible light irradiation. The self-modification strategy articulated in this study has strong potential for the creation of customized g-C₃N₄ band structures with enhanced oxidation performance.

Improving photocatalytic activity by construction of immobilized Z-scheme CdS/Au/TiO2 nanobelt photocatalyst for eliminating norfloxacin from water

To improve the photocatalytic activity of TiO₂ NBs under irradiation of solar light, an immobilized Z-scheme composite photocatalyst CdS/Au/TiO₂ NBs has been constructed. For the unique architectures, the TiO₂ NBs provide more absorption and reaction sites, the CdS nanoparticles enhance overall light harvesting, and Au acts as the electron transfer mediator, promoting the interfacial charge transfer and efficient separation of electrons and holes. The morphology, elements, crystal structure, optical and photoelectrochemical properties, and photocatalytic activity of CdS/Au/TiO₂ NBs were characterized. Results showed that CdS/Au/TiO₂ NBs possesses higher photocatalytic activity toward the degradation of antibiotic norfloxacin under irradiation of simulated sunlight, which is attributed to the synergetic interaction of increased light absorption and separation of photogenerated electrons and holes. Besides, the degradation of norfloxacin was promoted by HCO₃^-, but inhibited by NO₃^- and Cl^-. The radicals trapping experiments proved that superoxide radicals (O₂^-) was the dominating active species during the photocatalysis process. The photocatalytic degradation products of norfloxacin was analyzed, and nine intermediates were identified. Moreover, the photocatalytic degradation mechanism and photostability of CdS/Au/TiO₂ NBs were analyzed in detail. The matched energy levels and unique ternary Z-scheme design are the key for improved photocatalytic activity. The deactivation of CdS/Au/TiO₂ NBs after recycles mainly due to the release of CdS by photocorrosion and the loss of deposited Au.

Photocatalytic water splitting for hydrogen generation driven by tetragonal, trigonal, hexagonal and cubic LiCoO2 and visible light

The photocatalytic properties of LiCoO₂ are not explored up to date although its cubic and trigonal structures are explored experimentally. Here, we investigate the feasibility of photocatalytic hydrogen production from water splitting driven by the tetragonal, trigonal, hexagonal and cubic LiCoO₂ with the irradiation of the visible light. The band structure, density of state, optical absorption and mobility are calculated by the first-principles density functional theory. The results show that the band edges of all the four structures of LiCoO₂ match to the conditions of the redox potentials of water splitting reaction and the enhanced optical absorption in the visible light range is observed. The obvious difference between the mobilities of the hole and electron are identified, especially for the cubic LiCoO₂. All the obtained results suggest that the considered structures of LiCoO₂ are promising candidates for the photocatalytic water splitting to produce hydrogen with the irradiation of the visible light.

Study of the photodegradation of 2-chlorobenzoic acid by TiO2 and the effects of eutrophicated water on the reaction

The photodegradation of 2-chlorobenzoic acid (2-CBA) in suspensions of TiO₂ was examined under different operational parameters. The optimal condition could be obtained through the experiment, i.e. that the concentration of 2-CBA was 30 mg/L and the dosing quantity of TiO₂ was 0.01 g under UV light in the case of pH 3.5. Above reaction process was in accordance with first order kinetics model. The influence on photocatalytic degradation caused by typical anions in eutrophicated water body such as NO₃ ^- and H₂PO₄ ^- was explored in this work, which revealed that both two anions had inhibitory effect on the degradation process. In addition, alcohol was introduced into the process to identify the degradation mechanism of 2-CBA with TiO₂, and the reaction route of 2-CBA could be predicted through the analysis on the intermediate.

Green synthesis of copper nanoparticles using Celastrus paniculatus Willd. leaf extract and their photocatalytic and antifungal properties

This research aimed to explore the eco-friendly green synthesis of copper nanoparticles (CuNPs) using Celastrus paniculatus leaves extract. Primarily, the biosynthesized CuNPs characterized by UV-vis spectroscopy showed an absorption peak at 269 nm. Further, The SEM and TEM studies revealed the spherical shape of particles with size ranged between 2-10 nm with an average particle diameter of 5 nm. FT-IR analysis confirmed the presence of functional groups -OH, C[bond, double bond]C and C-H triggers the synthesis of CuNPs. The negative zeta potential -22.2 mV indicated the stability of CuNPs was confirmed by DLS and the composition and purity by EDS studies. Further, the photocatalytic property of the CuNPs was divulged by their methylene blue dye degradation potential. The reaction kinetics followed pseudo-first-order with k-values (rate constant) 0.0172 min-1. In addition, this material was found to be a good antifungal agent against plant pathogenic fungi Fusarium oxysporum showed 76.29 ± 1.52 maximum mycelial inhibition.

Two-Dimensional Platinum Diselenide: Synthesis, Emerging Applications, and Future Challenges

In recent years, emerging two-dimensional (2D) platinum diselenide (PtSe2) has quickly attracted the attention of the research community due to its novel physical and chemical properties. For the past few years, increasing research achievements on 2D PtSe2 have been reported toward the fundamental science and various potential applications of PtSe2. In this review, the properties and structure characteristics of 2D PtSe2 are discussed at first. Then, the recent advances in synthesis of PtSe2 as well as their applications are reviewed. At last, potential perspectives in exploring the application of 2D PtSe2 are reviewed.

Graphene oxide as a cartridge enable on-line assembly of photosensitizer for 1O2-based electrochemical aptasensing

An ultrasensitive ¹O₂-based electrochemical aptasensor by on-line assembly of photosensitizers using graphene oxide (GO) as a cartridge is reported. In the presence of target protein lysozyme, the interaction of lysozyme with aptamer led to the dissociation of dsDNA and release of the aptamer-lysozyme complex to solution, with DNA-c retaining on the electrode; then, the photosensitizer phloxine B (PB) was assembled on the electrode since GO can simultaneously adsorb DNA-c and PB molecules. Upon irradiation by a green LED, ¹O₂ was generated by photocatalysis of PB molecules and then cleaved the DNA-c, leading to remarkably decreased impedance signals that linearly respond with the logarithm of lysozyme concentration. Benefitting from the efficient photosensitization ability of PB and the high PB-loading capacity of GO, the developed sensor allowed determination of 0.001 to 100 nM lysozyme with a limit of detection of about 0.14 pM. The relative standard deviation (RSD) for five independent electrodes with 1 nM lysozyme was 3.1%, indicating satisfactory reproducibility. The sensor also showed excellent selectivity toward lysozyme in the presence of interfering substances and was applied to the determination of lysozyme in urine samples with recoveries ranging from 91 to 101%. The on-line assembly of photosensitizer technique opens a new way for amplified electrosensing of biomolecules. Graphical abstract An on-line assembly of photosensitizers and DNA on electrode was developed using graphene oxide a cartridge and the photocatalytic electrosensor can be used for label-free detection of lysozyme as low as 1 pM.

Photocatalytic activity and antibacterial efficacy of UVA-treated titanium oxides

Studies have shown ultraviolet-A (UVA) irradiation of crystalline titanium oxides leads to the production of reactive oxygen species (ROS) via a photocatalytic process. The ROS exhibit antimicrobial properties that may be of benefit in preventing bacterial attachment to implant devices. Recent studies have suggested a potential benefit of mixed anatase and rutile oxides and dopants on the photocatalytic properties of titanium oxides. The goal of this work was to compare the photocatalytic activity of different anodized commercially pure titanium grade 4 (CPTi4) surfaces. CPTi4 specimens were anodized in three mixed-acid electrolytes to create crystalline oxide surfaces that were either primarily anatase, primarily rutile, or a combination of anatase and rutile. Additionally, the primarily anatase and combination oxides incorporated some phosphorous from the phosphoric acid component in the electrolyte. The photocatalytic activity of the anodized specimens was measured using both methylene blue (MB) degradation assay and comparing the attachment of S. aureus under irradiation with UVA light of differing intensities (1 mW/cm², 8 mW/cm², and 23 mW/cm²). Primarily rutile oxides exhibited significantly higher levels of MB degradation after exposure to 1 mW/cm² UVA lights. Primarily rutile specimens also had the largest reduction in bacterial attachment followed by the mixed phase specimens and the primarily anatase specimens at 1 mW/cm² UVA lights. Phosphorous-doped, mixed phase oxides exhibited an accelerated MB degradation response during exposure to 8 mW/cm² and 23 mW/cm² UVA lights. All anodized and unanodized CPTi4 groups revealed similar S. aureus attachment at the two higher UVA intensities. Although MB degradation assay and the bacteria attachment assay both confirmed photocatalytic activity of the oxides formed in this study, the results of the MB degradation assay did not accurately predict the oxides performance against S. aureus.

Visible light responsive CuS/ protonated g-C3N4 heterostructure for rapid sterilization

As the environment deterioration is becoming more serious, bacterial pollution is threatening the health of human beings. Hence, it is vital to develop rapid and safe sterilization strategy. Herein, CuS/protonated g-C₃N₄(CuS/PCN) composites were synthesized by simple hydrothermal method and electrostatic adsorption. This heterostructured system exhibited enhanced photocatalytic properties under visible light compared with CuS or g-C₃N₄ alone, ascribing to the rapid separation of photogenerated electron-hole pairs. Meanwhile, the obvious photothermal effects of CuS/PCN were achieved and the temperature increased with the increased amount of CuS in the composites due to the more light absorption. However, when the CuS content is more than 10 %, photocurrent density is decreased with increasing the amount of CuS, indicating the increased recombination of photogenerated electron-hole pairs. When the CuS content is 20 %, the composite can perform the optimized synergistic effects of both photothermal action and photocatalysis under light irradiation for 20 min. The corresponding bacteria-killing efficiency against Staphylococcus aureus and Escherichia coli is 98.23 % and 99.16 %, respectively. The underlying mechanism is that the bacterial membrane can be weakened by reactive oxygen species and bacterial activities are inhibited by hyperthermia. This CuS/PCN heterojunction is promising for environmental disinfection including water and public facilities sterilization.

Fabrication and investigation on Ag nanowires/TiO2 nanosheets/graphene hybrid nanocomposite and its water treatment performance

In this paper, a novel Ag nanowires/TiO₂ nanosheets/graphene nanocomposite was fabricated via a facile method of hydrothermal and calcination, and then the water treatment performance of it was evaluated for methylene blue (MB) and Escherichia coli removal. The as-prepared Ag nanowires/TiO₂ nanosheets/graphene nanocomposite was characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), UV-visible diffuse reflection spectroscopy (DRS), molecular dynamics simulation, and gas chromatography-mass spectrometry (GC-MS). All data revealed that the Ag/TiO₂/graphene nanocomposite showed a rich cell structure. The photocatalytic activity of Ag/TiO₂/graphene nanocomposite is higher than those of pristine TiO₂ nanosheets and TiO₂/graphene nanocomposite. Under optimized conditions, the degradation efficiency was 100% and 71% for MB (30 mg/L) and with 10 mg Ag/TiO₂/graphene nanocomposite under UV and visible light irradiation for 2 h, respectively. Ag/TiO₂/graphene also showed excellent bacteria-killing activity. Meanwhile, the Ag/TiO₂/graphene nanocomposite exhibited microstructure stability and cyclic stability. The water treatment performance was enhanced mainly attributed to the excellent adsorption performance of graphene and the high efficiency in separation of electron-hole pairs induced by the remarkable synergistic effects of TiO₂, Ag, and graphene. On the basis of the experimental results, the photocatalytic mechanism and MB degradation mechanism were proposed. It is hoped that our work could avert the misleading message to the readership, hence offering a valuable source of reference on fabricating composite photocatalyst with stable microstructure and excellent performance for their application in the environment clean-up. Graphical abstract.

Novel visible light-responsive graphene oxide/Bi2WO6/starch composite membrane for efficient degradation of ethylene

Graphene oxide/Bi₂WO₆ (GBW) photocatalyst was synthesized using a hydrothermal and surface deposition method. GBW/starch composite films with different graphene oxide (GO) additions (0, 0.25, 0.5, 0.75, 1 %) were prepared using a casting method. The GBW photocatalyst and composite starch film were characterized using X-ray diffractometry, X-ray photoelectron spectroscopy, Ultraviolet-visible diffuse reflectance spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, synchronous thermal analyzer, and the capacity of photocatalytic degradation of ethylene under visible light was evaluated. The results showed that GBW strengthens the mechanical properties, water vapor resistance and thermal stability of the composite film. Proper introduction of GO can refine lattice size, reduce bandgap and enhance visible light absorption. When the addition of GO was 0.5 %, GBW/starch composite film showed the strongest visible light degradation activity for ethylene, and the rate constant K' was 9.91 × 10^-4 min^-1, 4.4 times that of pure Bi₂WO₆. The composite film also had good recycling performance.

Fabrication and Photocatalytic Activity of Ag3PO4/T-ZnOw Heterostructures

The Ag₃PO₄/tetrapod-like ZnO whisker (T-ZnOw) heterostructures were prepared via a simple precipitation method. The obtained heterostructures were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflectance spectroscopy. The photodegradation activity of Ag₃PO₄/T-ZnOw was evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation. When the molar ratio of Ag₃PO₄ to T-ZnOw was 10% (Ag₃PO₄/T-ZnOw-2), the highest degradation efficiency (92.9%) could be achieved among the heterostructures. The photodegradation rate constant of Ag₃PO₄/T-ZnOw-2 (0.05179 min^-1) was 3.59 times that of T-ZnOw (0.01444 min^-1). Besides, the Ag₃PO₄/T-ZnOw-2 photocatalyst still possessed a degradation efficiency of 77.8% after four successive cycles. The Ag₃PO₄/T-ZnOw-2 catalyst had much higher photocatalytic activity than pure T-ZnOw and better stability and reusability than pure Ag₃PO₄. The effect of different scavengers on degradation efficiency was investigated, and the possible photocatalytic mechanism of the Ag₃PO₄/T-ZnOw photocatalyst was also put forward.

Ce and Er Co-doped TiO2 for rapid bacteria- killing using visible light

Bacterial infection and related diseases are threatening the health of human beings. Photocatalytic disinfection as a simple and low-cost disinfection strategy is attracting more and more attention. In this work, TiO2 nanoparticles (NPs) were modified by co-doping of Ce and Er using the sol-gel method, which endowed TiO2 NPs with enhanced visible light photocatalytic performance but not pure ultraviolet photocatalytic properties compared the untreated TiO2. Our results disclosed that as the doping content of Er increased, the photocatalytic activity of modified TiO2 NPs initially increased and subsequently decreased. The same trend occurred for Ce doping. When the doping dose of Er and Ce is 0.5 mol% and 0.2 mol%, the 0.5Ce0.2Ti-O calcined at 800 °C presented the best antibacterial properties, with the antibacterial efficiency of 91.23% and 92.8% for Staphylococcus aureus and Escherichia coli, respectively. The existence of Er ions is thought to successfully turn the near-infrared radiation into visible region, which is easier to be absorbed by TiO2 NPs. Meanwhile, the addition of Ce ions can effectively extend spectral response range and inhibit the recombination of electrons and holes, enhancing the photocatalytic disinfection activity of co-doped TiO2.

Photocatalytic removal of elemental mercury via Ce-doped TiO2 catalyst coupling with a novel optical fiber monolith reactor

Reduction of mercury emission from coal combustion is a serious task for public health and environmental societies. Herein, Ce-doped TiO₂ (Ce/TiO₂) catalyst coupling with a novel optical fiber monolith reactor was applied to efficiently remove elemental mercury (Hg⁰) from coal-fired flue gas. Under the optimal operation condition (i.e., 1.5 mW/cm² UV light, 90 °C), above 95% of Hg⁰ removal efficiency was attained over the optical fiber monolith reactor coating with 3.40 g/m² Ce/TiO₂ catalyst. The effects of flue gas compositions on Hg⁰ removal performance were clarified systematically. Gaseous O₂ replenished the surface oxygen, hence maintaining the production of free radicals and promoting the removal of Hg⁰. SO₂, HCl, and NO inhibited Hg⁰ removal in the absence of O₂ due to the competitive adsorption and consumption of free radicals. However, SO₂ and HCl significantly enhanced Hg⁰ removal with the participation of O₂, while NO exhibited obviously inhibitory effect even with the assistance of O₂. H₂O also decreased the Hg⁰ oxidation capacity owing to the competitive adsorption and reduction of HgO. The optical fiber monolith reactor exhibited much superior Hg⁰ removal capacity than the powder reactor. Utilization of Ce/TiO₂ catalyst coupling with an optical fiber monolith reactor provides a cost-effective method for removing Hg⁰ from coal-fired flue gas.

Solvothermal synthesis of multiwall carbon nanotubes/BiOI photocatalysts for the efficient degradation of antipyrine under visible light

Antipyrine (ANT), as a widely used relieve headache, fever anti-inflammatory pharmaceutical in medical treatment, is difficult to be removed completely in water. The application of photocatalytic removal of ANT is restricted to UV light irradiation (<5% of solar energy), and the degradation pathways of ANT require more theoretical evidence. In this study, a series of three dimensions (3D) hierarchical structure multiwall carbon nanotubes/bismuth oxyiodide (MWCNTs/BiOI) photocatalysts were systematically designed and firstly applied to remove ANT through visible light (>43% of solar energy) induced photodegradation. Consequently, the as-prepared MWCNTs/BiOI photocatalysts presented superior photocatalytic activities on ANT degradation with respect to that of BiOI under 60 min visible light irradiation (100% vs 82.2%). Especially, the enhanced photocatalytic mechanism on ANT was analyzed by morphology, optical and photo-electrochemical properties. Results revealed that the designed 3D micro-mesoporous structure could promote the diffusion of photogenerated electron-hole pairs, and the utilization of photoelectrons could be efficiently improved by MWCNTs (1.5 times). Furthermore, based on radicals scavenging experiments, the photogenerated hole (h⁺) and superoxide radical (O₂^-) were demonstrated as the dominant active species in ANT photocatalytic oxidation process. The photodegradation pathways of ANT were proposed with the calculation of frontier electron densities (FEDs) and the analysis of LC-MS/MS. This study presents a feasible approach for the high efficiency removal of trace pharmaceuticals under visible light photocatalytic process.

Three-dimensional flower-like shaped Bi5O7I particles incorporation zwitterionic fluorinated polymers with synergistic hydration-photocatalytic for enhanced marine antifouling performance

Herein, several novel composite films consisting of three-dimensional (3D) Bi₅O₇I flower-like shaped microsphere and zwitterionic fluorinated polymer (ZFP) were successfully fabricated with the aim of achieving high anti-fouling performance. The prepared Bi₅O₇I flower-like shaped microsphere particles with diameters in the range of 2∼3 μm were uniformly distributed on the surface and in the internal of ZFP. Benefiting from the hydration layer formed by the ZFP and the efficient photocatalytic performance of Bi₅O₇I flower-like microsphere, the resultant optimized Bi₅O₇I/ZFP composite film exhibited an excellent diatom anti-settling performance and a high antibacterial rate of 99.09% and 99.66% towards Escherichia coli and Staphylococcus aureus. In addition, the composite films possessed the strengthened visible light absorption, the effectively separation and transfer of the photo-induced electrons and holes, the large number of hydroxyl (OH) radicals and superoxide radicals (O₂^-) all in Bi₅O₇I/ZFP systems, all of which were beneficial for the photocatalytic antifouling activity. More importantly, the synergistic hydration-photocatalytic effect of the Bi₅O₇I/ZFP composite films are answerable for the improvement of the antifouling property compared to the control. Thus, the synergistic hydration-photocatalytic contribution of Bi₅O₇I/ZFP composite film will shows promise for potential application in marine antifouling.

Performance optimization of CdS precipitated graphene oxide/polyacrylic acid composite for efficient photodegradation of chlortetracycline

Here a CdS embedded poly acrylic acid (PAA)/graphene oxide (GO) polymeric composite was prepared for the efficient degradation of chlortetracycline (CTC) driven by visible light irradiation. The structure-activity relationship of GO/PAA-CdS was confirmed through the photocatalytic evaluation of a series of samples prepared by varying GO concentration, molar ratio of Cd:S and the amount of crosslinking agent. Through the composition, morphology, photoelectrochemical characterizations and degradation kinetic studies, it could be confirmed that the enhanced photocatalytic activity is attributed to the controlled growth of CdS nanoparticles by polymer net structure and effective electron transfer along GO nanosheets. The photodegradation of CTC was confirmed to be mainly governed by O₂^- and OH radicals generated from GO/PAA-CdS. The degradation intermediates of CTC were confirmed by LC-MS, and possible degradation pathways were proposed based on the prediction of radical attacking sites according to Fukui function values obtained through Density Functional Theory (DFT). Moreover, it was found that the catalytic activity of the photocatalyst was maintained after several cycles confirming the enhanced anti-photocorrosion of GO/PAA-CdS. This research provided an efficient approach by a novel photocatalyst for the removal of CTC from wastewater.

Simulated photocatalytic aging of biochar in soil ecosystem: Insight into organic carbon release, surface physicochemical properties and cadmium sorption

Photochemical/photocatalytic reaction, one of the aging pathway of biochar in soil, not only changed the physicochemical properties of biochar, but also affected the migration and transformation of pollutants. Wheat straw biochar was photocatalytic aged in a Fenton-like system using organic acid as buffer solution under light sources, the organic carbon release and surface chemical changes of biochar were investigated to illustrate the adsorption behaviors. With Fe(III) or α-Fe₂O₃ added, the total organic carbon (TOC) of aged biochar solution was influenced more by buffer system than light sources, with the highest of 420.59 mg L^-1 in citric acid system. The production of the hydroxyl radical (OH·) at citric/Fe(III) system was higher than the oxalic/Fe(III) system under the Hg lamp and showed an increasing trend with time. With light exposure, the porous structure of the biochar altered and surface area increased from 7.613 to 29.74 m² g^-1. Meanwhile, the adsorption of cadmium ion by biochar aged in citric/Fe(III) system also showed an increased adsorption capacity with a maximum of 73.54 mg g^-1. So, a well understanding of biochar physicochemical properties changes under natural ecosystem was undoubtedly useful for scientific assessment the long-term feasibility of biochar as soil remediation.

Highly active metal-free carbon dots/g-C3N4 hollow porous nanospheres for solar-light-driven PPCPs remediation: Mechanism insights, kinetics and effects of natural water matrices

Pharmaceuticals and personal care products (PPCPs) are increasingly being scrutinized by the scientific community due to their environmental persistence. Therefore, the development of novel environmentally compatible and energy-efficient technologies for their removal is highly anticipated. In this work, a novel metal-free photocatalytic nanoreactor was successfully synthesized by anchoring carbon dots to hollow carbon nitride nanospheres (HCNS/CDs). The unique structure of these hollow nanospherical HCNS/CDs hybrids endowed them with a high population of reactive sites, while enhancing optical absorption due to internal light reflection. Simultaneously, the CDs served as "artificial antennas" to absorb and convert photons with low energy, due to their superior up-converting properties. Consequently, the HCNS/CDs demonstrated excellent photodegradation activities for the degradation of PPCPs under broad-spectrum irradiation. Remarkedly, 10 mg/L of naproxen (NPX) was completely degraded following 5 min of natural solar irradiation. It was further revealed that the O₂^•- played a significant role during the photocatalytic process, which could lead to the decomposition of NPX. The effects of natural water matrices and the degradation of trace PPCPs further supported that this photocatalytic system may be efficaciously applied for the remediation of PPCPs contamination in ambient waterways.

Synthesis of a heterojunction CoTiO3/Co3O4 nano-composite thin film with superior photocatalytic activity and reusability: Effect of calcination temperature on phase transformation and effect of oxidants on enhanced degradation of Indo Light Blue dye

CoTiO₃/Co₃O₄ heterojunction nano-composite was grown by a coprecipitation method at low temperature. The effects of calcination temperature on the phase composition, crystallization and morphology of the cobalt titanates were also examined. Notably, the novel nano-crystalline cobalt titanate with a narrow band gap to coulpe with cobalt oxide (Co₃O₄) by a direct coprecipitation method (CoTiO₃/Co₃O₄) was attained. The Nano-crystalline samples were systematically characterized by TG/DTG, XRD, DRS, FESEM, FT-IR, EDX and XPS techniques. The results showed that CoTiO₃/Co₃O₄ nano-composite hetero-junction was formed at 650 °C, while at 750 °C a single phase CoTiO₃ nano-crystal was prepared. Photocatalytic activities indicated the heterostructured CoTiO3/Co₃O₄ nano-composite exhibited much higher photocatalytic activity for degradation of Indo Light blue under visible light irradiation with added oxidants (K₂S₂O₈, KBrO₃, and H₂O₂). The charge separation of CoTiO3 and Co₃O₄ would result the enhanced visible-light harvesting ability and longer lifetime of photogenerated charge carriers. The stability and reusability of catalysts during four successive cycles were resulted. Finally, a possible mechanism responsible for the charge separation and improved photocatalytic activity was proposed.

Photocatalytic degradation of sulfamethazine using a direct Z-Scheme AgI/Bi4V2O11 photocatalyst: Mineralization activity, degradation pathways and promoted charge separation mechanism

Z-scheme heterojunction can not only promote the separation of photogenerated carriers, but also retain the strong redox potential of the system, which would greatly improve the photocatalytic performance of catalyst. Herein, a Z-scheme AgI/Bi₄V₂O₁₁ heterojunction photocatalyst was prepared by a hydrothermal process combined with in situ coprecipitation process. Multiple techniques were employed to investigate the morphology, composition, chemical and electronic properties of the as-prepared samples. The obtained Z-scheme AgI/Bi₄V₂O₁₁ heterojunction photocatalyst exhibited remarkably enhanced photocatalytic performance towards sulfamethazine (SMZ) degradation under visible light irradiation. Especially, the 20 wt% AgI/Bi₄V₂O₁₁ composites exhibited the highest photocatalytic activity for sulfamethazine (SMZ) degradation and 91.47% SMZ would be eliminated within 60 min. In comparison with NO₃^- and SO₄^2-, the presence of Cl^- and HCO₃^- presented more obviously inhibition effects on SMZ degradation. The possible degradation pathways of SMZ were speculated by identifying degradation intermediates. O₂^-, h⁺ and OH all involved in the photocatalytic degradation SMZ. The highly enhanced photocatalytic performance might be attributed to form Z-scheme junction between AgI and BVO, which are conducive to the efficient charges separation and maintain high redox potential. This work enriches Bi₄V₂O₁₁-based Z-scheme heterojunction photocatalytic system and provides a reference for the preparation of effective Z-scheme junction photocatalysts.

Construction of ultrathin MoS2/Bi5O7I composites: Effective charge separation and increased photocatalytic activity

Ultrathin MoS₂ nanosheet hybridized Bi₅O₇I (MoS₂/Bi₅O₇I) nanorods were synthesized via a reactable ionic liquid assisted solvothermal process for the first time. The photocatalytic activity of MoS₂/Bi₅O₇I nanorods was determined by photodegrading bisphenol A (BPA), tetracycline hydrochloride (TC) and ciprofloxacin (CIP) under visible light irradiation. Experimental results showed that MoS₂/Bi₅O₇I owned the excellent photocatalytic properties and photostability. The efficient visible light driven photocatalytic performance was due to a larger specific surface area of MoS₂, which increased the close interfacial contact between pollutants and photocatalysts. Meanwhile, the introduction of ultrathin MoS₂ nanosheet was conducive to the separation and utilization of photoinduced charge carriers, thus further suppressed high recombination rate in pure Bi₅O₇I nanorods. Moreover, a possible charge transfer path in MoS₂/Bi₅O₇I composite material was also put forward.

Photo-responsive chitosan/Ag/MoS2 for rapid bacteria-killing

Bacterial infection is a serious problem threatening human health. The chitosan (CS)-modified MoS₂ coating loaded with silver nanoparticles (Ag NPs) was designed on the surface of titanium (Ti) to kill bacteria rapidly and efficiently under 660 nm visible light. Ag/MoS₂ exhibited high photocatalytic activity due to the rapid transfer of photo-inspired electrons from MoS₂ to Ag NPs, resulting in higher yields of radical oxygen species (ROS) to kill bacteria. The covering of CS made the composite coating positively charged to further enhance the antibacterial property of the coating. In addition, CS/Ag/MoS₂-Ti also showed a certain photothermal effect. in vitro results showed that the antibacterial efficiency of the coating on Staphylococcus aureus and Escherichia coli was 98.66% and 99.77% respectively, when the coating was irradiated by 660 nm visible light for 20 min. Cell culture tests showed that CS/Ag/MoS₂-Ti had no adverse effects on cell growth. Hence, this surface system will be a very promising strategy for eliminating bacterial infection on biomedical device and implants safely and effectively within a short time.

Oxygen vacancy rich Bi2O4-Bi4O7-BiO2-x composites for UV-vis-NIR activated high efficient photocatalytic degradation of bisphenol A

To fully utilize the solar light, photocatalyst with broad spectrum response from UV to near-infrared (NIR) is desirable. In this work, ternary mixed valent Bi₂O₄-Bi₄O₇-BiO_2-x with rich oxygen vacancy has been synthesized through one-pot hydrothermal treatment of NaBiO₃. The results showed that through adjusting the hydrothermal conditions, oxygen vacancy-rich Bi₂O₄-Bi₄O₇-BiO_2-x nanocomposites with much higher efficiency than single or mixed bismuth oxides (Bi₂O₄, Bi₄O₇, BiO_2-x and Bi₄O₇-BiO_2-x,) can be synthesized for photocatalytic degradation of bisphenol A (BPA) under UV, visible, and NIR light irradiation. In addition, the liquid chromatography-mass spectrometer (LC-MS) characterization demonstrated that BPA was oxidized to 4-isopropenyphenol first and the rings were opened sequentially under NIR light irradiation. Further detection of reactive species indicated that holes, O₂^-, and OH were the main oxidizing species in the degradation system. The experimental observations and density functional theory (DFT) calculations suggested that both type-II and the Z-scheme charge transfer with oxygen vacancies as electrons and holes mediators were formed at the interfaces of Bi₂O₄, Bi₄O₇, and BiO_2-x, resulting in a very efficient separation of photogenerated charge carriers in the composite. This work adds to the growing potential of mixed valent bismuth oxides based photocatalysts and is expected to accelerate the pace of the development of new-generation photocatalysts with high efficiency utilizing full-spectrum solar light.

One-step synthesis of carbon dots for selective bacterial inactivation and bacterial differentiation

Novel carbon dots (CDs) were synthesized by a one-pot hydrothermal approach using ampicillin as a precursor, and the as-prepared CDs exhibited a high quantum yield (23%). The CDs were found to possess abundant surface functional groups, thus providing good permeability to the cell, and the antibacterial activity of CDs was evaluated. S. aureus and L. monocytogenes were selected as model bacteria, and our results showed that the CDs exhibited antibacterial activity against S. aureus and L. monocytogenes under visible light illumination, even at low concentrations. The antibacterial mechanism is believed to be the production of reactive oxygen species (ROS) from CDs under visible light irradiation, which attacked the bacterial cell membranes, resulting in the death of the bacteria. In addition, because of the multicolor fluorescence properties of CDs, staining of S. aureus and L. monocytogenes obtained multicolor fluorescence images at different excitation wavelengths. Based on these results, CDs are a promising candidate material for biological applications. Graphical abstract.

Superimposed surface plasma resonance effect enhanced the near-infrared photocatalytic activity of Au@Bi2WO6 coating for rapid bacterial killing

Bacterial infection has become a serious public health challenge because the misuse of antibiotics worldwide has induced bacterial resistance and superbug occurrences, that is, no suitable antibiotics are available. Herein, we design a new infrared photocatalytic system on titanium (Ti) substrates, and it consists of gold (Au) nanorod-decorated bismuth tungstate (Bi₂WO₆) nanosheets (Au@Bi₂WO₆). The surface plasmon resonance (SPR) effect induced by near infrared (NIR) facilitates partial photo-induced electron transfer between Au and Bi₂WO₆, resulting in accelerated charge transmission and consequently hindering electron-hole recombination, which imparts high photocatalytic property to the coating. In addition, the superimposed SPR from both Au and Bi₂WO₆ can improve the photothermal effect of Au@Bi₂WO₆. As a result, when irradiated with 808 nm NIR for 15 min, this hybrid coating exhibits a superior antibacterial efficiency of 99.96% and 99.62% against Escherichia coli and Staphylococcus aureus, respectively, due to the synergistic effects of high yield of radical oxygen species and hyperthermia; this efficiency cannot be achieved by either Au-Ti or Bi₂WO₆-Ti alone. This platform exhibits a great potential for noninvasive disinfection without using antibiotics.

Surface modified of polyacrylonitrile nanofibers by TiO2/MWCNT for photodegradation of organic dyes and pharmaceutical drugs under visible light irradiation

This work describes the fabrication of two composite nanofibers systems containing polyacrylonitrile polymer (PAN), Multiwall carbon nanotubes (MWCNT) and Titania (TiO₂) nanoparticles. Photodegradation experiments were performed to study the effect of various parameters including pH, catalyst dose, pollutant concentration and reaction time for three model compounds, methylene blue (MB), indigo carmine (IC), and ibuprofen (IBU) under visible light. Morphology and structure of the modified composite nanofibers were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Thermogravimetric analysis (TGA), Photoluminescence (PL) spectroscopy, Raman spectra, and X-ray Photoelectron Spectra (XPS) analyses. The photocatalytic performance was achieved in a rather short time visible light (<30 min) and under low power intensity (125 W) compared to earlier reports. Kinetics data fitted well using pseudo-first order model to describe the mechanism of photocatalytic degradation processes. The stability and flexibility of the fabricated composite nanofibers allow their application in a continuous flow system and their re-use after several cycles.