Silver nanoparticles (AgNPs) are widely used in consumer products due to their antibacterial property; however, their potential toxicity and release into the environment raises concern. Based on the limited understanding of AgNPs aggregation behavior, this study aimed to investigate the toxicity of uncoated (uc-AgNP) and coated with polyvinylpyrrolidone (PVP-AgNP), at low concentrations (0.5–100 ng/mL), under dark and visible-light exposure, using a plant test system. We exposed Allium cepa seeds to both types of AgNPs for 4–5 days to evaluate several toxicity endpoints. AgNPs did not cause acute toxicity (i.e., inhibition of seed germination and root development), but caused genotoxicity and biochemical alterations in oxidative stress parameters (lipid peroxidation) and activities of antioxidant enzymes (superoxide dismutase and catalase) in light and dark conditions. However, the light exposure decreased the rate of chromosomal aberration and micronuclei up to 5.60x in uc-AgNP and 2.01x in PVP-AgNP, and 2.69x in uc-AgNP and 3.70x in PVP-AgNP, respectively. Thus, light exposure reduced the overall genotoxicity of these AgNPs. In addition, mitotic index alterations and morphoanatomical changes in meristematic cells were observed only in the dark condition at the highest concentrations, demonstrating that light also reduces AgNPs cytotoxicity. The light-dependent aggregation of AgNPs may have reduced toxicity by reducing the uptake of these NPs by the cells. Our findings demonstrate that AgNPs can be genotoxic, cytotoxic and induce morphoanatomical and biochemical changes in A. cepa roots even at low concentrations, and that visible-light alters their aggregation state, and decreases their toxicity. We suggest that visible light can be an alternative treatment to remediate AgNP residues, minimizing their toxicity and environmental risks.

A novel Z-scheme photocatalyst consisting of acidified graphitic carbon nitrogen (ag-C₃N₄)/carbon quantum dots/CdIn₂S₄ (CN/CQDs/CIS) was successfully synthesized via a one-step hydrothermal method. The optimized CN-2/CQDs-3/CIS exhibited significantly improved photocatalytic performance in the degradation of ibuprofen under visible-light irradiation. Based on a series of characterizations, the ag-C₃N₄ and CQDs were distributed uniformly on the surface of the cubic spinel structure of CIS, with intimate contact among the materials. This intimate heterogeneous interface facilitated the migration of photogenerated carriers, further leading to enhanced photocatalytic performance. These results also indicated that the CQDs not only connect ag-C₃N₄ with CIS through covalent bonds but also enhance the visible-light adsorption. According to the analysis of the UV–vis diffuse reflectance spectra (DRS) and Mott-Schottky curves, the mechanism of the Z-scheme heterojunction is proposed. The CQDs serve as electron mediators and transfer the electrons in the conduction band (CB) of ag-C₃N₄ to recombine with the holes in the valence band (VB) of CIS in the Z-scheme, leading to the enhanced separation efficiency of the photogenerated electrons in the CB of ag-C₃N₄ and the holes in the VB of CIS. The pollutant IBU was degraded by h⁺, ·O₂⁻ and ·OH, as determined by electron paramagnetic resonance (EPR) analysis.

Surface functionalization and shape modifications are the key strategies being utilized to overcome the limitations of semiconductors in advanced oxidation processes (AOP). Herein, the uniform α-Fe₂O₃ nanocrystals (α-Fe₂O₃–NCs) were effectively synthesized via a simple solvothermal route. Meanwhile, the sulfonic acid functionalization (SAF) and the impregnation of α-Fe₂O₃–NCs on g-C₃N₄ (α-Fe₂O₃–NCs@CN-SAF) were achieved through complete solvent evaporation technique. The surface functionalization of the sulfonic acid group on g-C₃N₄ accelerates the faster migration of electrons to the surface owing to robust electronegativity. The incorporation of α-Fe₂O₃–NCs with CN-SAF significantly enhances the optoelectronic properties, ultrafast spatial charge separation, and rapid charge transportation. The α-Fe₂O₃-HPs@CN-SAF and α-Fe₂O₃-NPs@CN-SAF nanocomposites attained 97.41% and 93.64% of Cr (VI) photoreduction in 10 min, respectively. The photocatalytic efficiency of α-Fe₂O₃–NCs@CN-SAF nanocomposite is 2.4 and 2.1 times higher than that of pure g-C₃N₄ and α-Fe₂O₃, respectively. Besides, the XPS, PEC and recycling experiments confirm the excellent photo-induced charge separation via Z-scheme heterostructure and cyclic stability of α-Fe₂O₃–NCs@CN-SAF nanocomposites.

Pieces of glass as solid wastes were recycled in the synthesis of highly order MCM-41 that decorated by green fabricated Co₃O₄ nanoparticles using the green extract of green tea leaves forming novel green nano-composite. The synthetic Co₃O₄/MCM-41 exhibit high surface area, low bandgap energy (1.63 eV), and typical spherical morphology decorated by Co₃O₄ nanoparticles. The composite was evaluated as green photocatalyst in effective oxidation of methyl parathion pesticide in the presence of a visible light source. The degradation results revealed complete removal of 50 mg/L and 100 mg/L after 60 min and 90 min, respectively using 0.25 of the catalyst at pH 8. The detection of the TOC in the treated methyl parathion solution gives strong indications about the formation of organic intermediate compounds during the oxidation steps. The main detected intermediate compound are C₆H₅OH(NO₂), C₆H₅OH, (CH₃O)₃P(S), C₆H₄(OH)₂, C₆H₃(OH)₃, C₆H₄(NH₂)OP(O)(OCH₃)₂, (CH₃O)₂P(O)OH, (CH₂)₂C(OH)OH(CHO)OC(O), and HO₂C(CH₂)₂C(O)CHO. The detected intermediate compounds converted into SO₄²⁻, PO₄³⁻, NO₃⁻, and CO₂ under the extensive photocatalytic of them over Co₃O₄/MCM-41. The oxidizing species trapping test verified the controlling of the methyl parathion degradation pathway by the hydroxyl radicals. Finally, the composite showed significant reusability properties and applied five times in the oxidation of methyl parathion with considerable degradation percentages.

Photocatalysis is a promising method to eliminate hexavalent uranium (U(Ⅵ)) and recycle it from wastewater. However, most of researched photocatalysts are metal-contained, inactive in visible light, and inconvenient to recycle, which unfortunately impedes the further utilization of photocatalytic technology in U(Ⅵ) pollution treatment. Herein, g-C₃N₄ isotype heterojunction with interpenetrated tri-s-triazine structure (ipCN) was prepared by inserting urea into the interlayer of tri-s-triazine planes of thiourea-derived g-C₃N₄ and in-site thermal treating. The synthesized nanocomposites were used to convert soluble U(Ⅵ) ions into U(Ⅳ) sediment under visible light. Experimental and characterization results reveal that ipCN possess larger BET surface area, more negative-charged surface, higher U(Ⅵ) adsorption capability, and more efficient mass diffusion and charges transfer properties. With these excellent characteristics, nearly 98% U(Ⅵ) could be removed within 20 min over ipCN₅:₁ and 92% photoreduction efficiency could also be kept after 7 cycle uses, which were equal to or even superior than most reported metal-based photocatalysts. It is also proven that the configuration of U(Ⅵ) and photogenerated ·O₂⁻ play a significant role in the photocatalytic U(Ⅵ) reduction process, with (UO₂)ₓ(OH)y²ˣ⁻ʸ are more prone to be adsorbed and the photoinduced process of ·O₂⁻ will steal electrons from photocatalysts. Furthermore, with the self-generated ·O₂⁻ and H₂O₂, a green and facile regeneration process of photocatalysts was proposed This work provides a promising scheme to extract U(Ⅵ) from the perspectives of photocatalysts exploitation, photocatalytic reduction, and photocatalysts regeneration, which is meaningful for the sustainable U(Ⅵ) resource recovery and U(Ⅵ) pollution purification.

A self-assembly method was adopted to synthesize loading architecture of ZnO/g-C₃N₄ heterojunction composites by hybridization of g-C₃N₄ nanosheets and ZnO nanoparticles utilizing a refluxing method at a low temperature. More importantly, we provided a novel route to regulate the π-π restacking thickness of the g-C₃N₄ nanosheets among ZnO/g-C₃N₄ composites by the controlling the refluxing time in the ethanol solution, which can optimize the surface hybrid structure, optical response and photocatalytic activity. Among all of samples, ZnO/g-C₃N₄ composites with a refluxing 12 h showed the enhancement of photocatalytic activity. The enhanced visible light photocatalytic activity of ZCN-12 composites can be ascribed to the synergistic effects of the construction of hybrid structures, reduction of structural defects of g-C₃N₄ nanosheets and suitable π-π restacking g-C₃N₄ nanosheets loading thickness.

The immobilized CdS/TiO₂ nanofiber (CdS/TiO₂ NF) heterostructure photocatalyst was fabricated via anodic oxidation and cyclic impregnation method. The microstructure of CdS/TiO₂ NF was characterized by SEM and TEM. The components of CdS/TiO₂ NF were identified by EDX, XPS, and Raman. The optical properties of CdS/TiO₂ NF were characterized by UV-vis DRS and PL. Results showed that CdS was loaded on the surface of TiO₂ NF in the form of particles with a diameter of about 10–80 nm. The Cd and S elements were detected on the surface of catalyst. CdS/TiO₂ NF improved the absorption performance in the ultraviolet and visible light regions and reduced the recombination of photogenerated electron-hole pairs. The performance of CdS/TiO₂ NF on degrading toluene was investigated. Results showed that the deposition of CdS enhanced the photocatalytic activity of TiO₂ NF. The toluene concentration, catalyst dosage, and flow rate had marked impact on the photocatalytic degradation efficiency of toluene. In this reaction system, the degradation ratio was 80.71% when the toluene concentration was 13 mg·L⁻¹, the photocatalyst area was 32 cm², the flow rate was 3 L·min⁻¹, and the illumination time was 100 min. The mineralization ratio after photocatalytic reaction for 100 min was about 45.02%. The immobilized CdS/TiO₂ NF photocatalyst is easy to be recycled, which can reduce the energy and material cost. This work not only highlights the intrinsical role of CdS materials in the enhanced photocatalytic performance of TiO₂ NF but also provides significant guidance on fabricating immobilized CdS/TiO₂ NF photocatalyst applied in environment remediation.

In this work, titanium dioxide nanoparticles (TiO₂ NPs) and modified TiO₂ NPs with silver (Ag) or platinum (Pt) dopant were developed through photodeposition method for the NOₓ conversion into nitric acid (HNO₃) under visible light irradiation. The formed photocatalysts TiO₂, Ag/TiO₂, and Pt/TiO₂ nanocomposites were characterized by utilizing TEM, SEM, energy-dispersive X-ray analysis (EDX), XRD, UV/visible diffuse reflectance spectroscopy (UV-Vis DRS), and FT-IR. It had been investigated that an enhancement within the conversion of NOₓ into HNO₃ was increased from 34.3 to 78.3% for Ag/TiO₂ and from 35.2 to 78.5% for Pt/TiO₂ under visible light irradiation conditions at room temperature for less than 2 h. The photodegradation rate order of NOₓ under visible light irradiation is Pt/TiO₂ ~ Ag/TiO₂ > TiO₂. A possible mechanism for the catalytic conversion of NOₓ gases has been proposed, which depends on the photogeneration of electrons and holes after the excitation of nanocatalysts under visible radiation that promoted superoxide and hydroxyl ions, which can depredate NOₓ gases. This approach of NOₓ photocatalytic conversion is characterized by its chemical stability, low cost, high efficiency, simple operation, and strong durability than traditional methods.

TiO₂-based heterogeneous photocatalysis systems have been reported with remarkable efficiency to decontaminate and mineralize a range of pollutants present in air and water medium. In the present study, a series of visible light active metal oxide TiO₂ nanoparticle were synthesized and evaluated for their photodegradation efficiency against emerging textile pollutant (Reactive Yellow 145) and antibacterial applications. In the first phase, nanomaterial synthesis was carried out following various synthesis parameters like addition of metallic impurities (different types and concentration) and calcination temperature. In the second phase, synthesized nanomaterials were screened for their performance in terms of photocatalytic degradation of RY145 and the best one (Fe-1-T-3 with 100% RY145 removal within 80 min of irradiation) was further optimized against various reaction parameters. To get knowledge about the insights of nanomaterial performance for degradation of different environmental pollutants, the most important is to understand their physicochemical properties utilizing different characterization techniques. The physical morphology and elemental dispersion of metal-doped TiO₂ nanomaterials were analyzed and results indicated that added metallic impurities were well dispersed onto the substrate surface. The efficient nanomaterials selected from initial screening were further assessed for photocatalytic disinfection efficiency against human pathogenic bacterial strains. Antimicrobial activities of the metal oxide nanomaterial were tested against gram-positive and gram-negative pathogenic bacterial strains. Possible mode of interaction of nanomaterial with bacterial DNA for bacterial cell inactivation was predicted using molecular docking simulation. The research project has the potential to contribute to multiple disciplines like material synthesis, water disinfection, and as green solutions for the textile industry replacing traditional technologies.

The harm of chromium pollution to the environment has caused a widespread concern; hexavalent chromium is a toxic, cancerogenic, and genetically mutagenic contaminant to the human body; by contrast, trivalent chromium is almost non-toxic to the human body; therefore, it is a feasible method to reduce hexavalent chromium to trivalent chromium. Photocatalysis is a new environmentally friendly and harmless technology, which can transform pollutants into non-toxic or less toxic products. In this study, we synthesized TiO₂/rGO/CuO ternary nanocomposites to treat hexavalent chromium pollution under visible light. Under optimal conditions, the photoreduction efficiency of 100 ppm hexavalent chromium solution could reach 100% in 80 min. The photoreduction rate of hexavalent chromium is 29.4 times than that of pure TiO₂. The photocatalytic property of CuO in TG2C8 nanocomposites is attributed to accelerate the separation of electrons and holes and the efficient electron transfer through the rGO framework. We believe that TiO₂/rGO/CuO composites have great potential in wastewater treatment.