Visible light responsive Mn-S-co-doped TiO 2 photocatalyst – Synthesis, characterization and mechanistic aspect of photocatalytic degradation

Hydrazine-Assisted Synthesis, Structures, Photoelectricity, and Photocatalysis of Ternary Mercury-Tellurostannate Hybrids with Transition-Metal Complexes

Tellurostannates are traditionally prepared by multistep reactions using the tellurides SnTe, SnTe2, K4SnTe4, or A6SnTe6 (A = K, Rb, or Cs) as precursors, which are usually prepared by the molten reaction of alkali metals Sn and Te under harsh synthetic conditions. Differently, ternary Hg-tellurostannate hybrids [Mn(en)3]HgSnTe3(Te2) (1) (en = ethylenediamine), [Mn(dien)2]HgSnTe3(Te2) (2), and [Fe(dien)2]HgSnTe3(Te2) (3) (dien = diethylenetriamine) were synthesized by one-pot reactions using Sn and Te powders as starting materials in the presence of hydrazine under mild solvothermal conditions. In 1, HgTe3 and SnTe4 units are joined via Te-sharing to form a 1-D polymeric chain [HgSnTe3(Te2)]n2n-, while the [HgSnTe3(Te2)]n2n- chains in 2 and 3 are composed of HgTe4 and SnTe4 units. The common feature of the [HgSnTe3(Te2)2-]n chains in 1-3 is that they are constructed by both the telluride anion Te2- and the polytelluride anion Te22-. 1-3 exhibited strong photocurrent responses with current densities of 5.26, 3.38, and 3.94 μA cm-2, respectively. They showed effective photocatalytic activities for methylene blue degradation with degradation ratios in the range of 85.3-94.6% after light irradiation for 80 min. Investigation of the photocatalytic mechanism showed that •O2- radicals and h+ holes were the main active substances in the photodegradation.

Photocatalytic Degradation of Ceftriaxone Using TiO2 Coupled with ZnO Micronized by Supercritical Antisolvent Route

Heterogeneous photocatalysis is a promising technique for removing pollutants from water. In this work, supercritical antisolvent (SAS)-micronized ZnO (ZnOSAS) is coupled with commercial anatase TiO2 (PC50) to study the photocatalytic degradation of ceftriaxone under UV and visible light. Diffuse ultraviolet-visible reflectance (UV-vis DRS) measurement revealed that the presence of ZnO leads to a slight absorption in the visible region. Wide-angle X-ray diffraction (WAXD) analysis showed the presence of both ZnO wurtzite and TiO2 anatase crystalline phases in the composite. Photocatalytic tests proved that the activity of the ZnOSAS/PC50 composite is higher than that of commercial ZnO, SAS-micronized ZnO, and PC50, allowing complete ceftriaxone degradation under UV light after only 2 min of irradiation time. In contrast, about 90% of ceftriaxone degradation is achieved after 180 min of visible-light irradiation. The photocatalytic results for an experiment carried out in the presence of probe scavenger molecules for reactive oxygen species show that hydroxyl radicals and positive holes are both reactive species involved in the ceftriaxone photocatalytic degradation mechanism. Finally, reuse cycles of the ZnOsas/PC50 composite are performed, demonstrating the stability and recyclability of the photocatalyst.

Eliminating pesticide quinalphos from surface waters using synthesized GO-ZnO nanoflowers: Characterization, degradation pathways and kinetic study

The presence of highly toxic and persistent pesticides in water bodies causes serious problems to human beings as well as aquatic life. Quinalphos is one such widely used organophosphorus pesticide in agricultural fields. Herein, for degradation and mineralization of quinalphos, ZnO nanoflowers and their hybrid nanocomposite with graphene oxide have been synthesized. FESEM analysis confirmed the formation of ZnO nanoflowers over nanosheets of graphene oxide having a thickness of 20 ± 10 nm. GO-ZnO composite exhibited remarkable photocatalytic activity in comparison to pure ZnO. 98 % degradation of quinalphos was achieved using GO-ZnO nano-catalyst at 6 pH within 45 min of irradiations, whereas it was 80 % for bare ZnO nanoflowers. Higher degradation with hybrid nanocomposite was attributed to improved surface area (36 m² g^-1), a substantial reduction in bandgap energy from 3.10 to 2.90 eV and enhanced charge separation (e^-/h⁺ pairs) after the addition of GO. Reaction kinetics study followed pseudo-first-order behaviour. Further, mineralization to the extent of 90 % in 90 min was confirmed by TOC analysis. Based on identified intermediates, using LCMS analysis, degradation pathways were proposed. The plausible pathways confirmed the presence of smaller and safer reaction intermediates supported by excitation of e^- from nanocomposite followed by oxidation of quinalphos with huge free radicals. Overall, this study is significant in terms of using photocatalysis as a tertiary treatment of quinalphos pesticide wastewater at pH 6 in a short duration.

A new Ru(ii) polypyridyl complex as an efficient photosensitizer for enhancing the visible-light-driven photocatalytic activity of a TiO2/reduced graphene oxide nanocomposite for the degradation of atrazine: DFT and mechanism insights

TiO₂ is one of the most widely used semiconductors for photocatalytic reactions. However, its wide bandgap energy and fast charge recombination limit its catalytic activity. Thus, herein, a new Ru(ii) polypyridyl complex, [Ruii(tptz)(CH₃CN)Cl₂] (tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine), was synthesized and used as a visible-light photosensitizer dye for improving the light harvesting and quantum efficiency of TiO₂. Accordingly, a well-designed nanostructured photocatalyst was proposed using mesoporous TiO₂ nanocrystals coupled with reduced graphene oxide (rGO) and the polypyridyl Ru(ii) complex, which was tested for the photocatalytic degradation of atrazine (ATZ) as a model of emerging water contaminants. Specifically, the Ru complex (Ru-CMP) served as an electron donor, while rGO acted as an electron acceptor, and the synergistic effect between them promoted the separation of electron–hole pairs and suppressed the charge recombination in the hybridized species. Structural analysis indicated that the TiO₂ nanoparticles with an anatase crystal structure had a mesoporous texture and were homogeneously coated on the rGO sheets. The detailed FT-IR, Raman, XPS and UV-vis absorption spectroscopic analyses combined with EDS mapping clearly confirmed the successful loading of the Ru complex onto the catalyst. The PL and EIS results revealed that the addition of the Ru-CMP photosensitizer enhanced the charge separation and transport. The gas-phase geometry and energies of the molecular orbitals of the Ru complex were evaluated via DFT calculations. The results from the DFT calculations were consistent with the experimental results. Compared to pure TiO₂, the as-synthesized Ru-CMP-TiO₂/rGO hybrid exhibited significantly enhanced photocatalytic activity for the degradation of ATZ. The rate of ATZ degradation in the developed photocatalytic process with the Ru-CMP-TiO₂/rGO hybrid was 9 times that with commercial TiO₂. The enhanced photocatalytic activity of the prepared catalyst can be attributed to its better light harvesting and efficient electron transportation due to its more suitable LUMO position than the conduction band of TiO₂. Moreover, the excellent conductivity and adsorption capacity of graphene contributed to the increase in photocatalytic activity. Thus, these features make the Ru-CMP-TiO₂/rGO hybrid nanomaterial an excellent candidate for the photocatalytic purification of contaminated water.

TiO₂ is one of the most widely used semiconductors for photocatalytic reactions.

Investigations on Amphoteric Chitosan/TiO2 Bionanocomposites for Application in Visible Light Induced Photocatalytic Degradation

The present investigation reports the greener synthesis and characterization of novel acrylic acid grafted amphoteric chitosan/TiO2 (CAT) bionanocomposites using ultrasonic radiations. This was done by grafting of acrylic acid onto chitosan in the presence of potassium persulfate by free radical polymerization reaction. The uniform distribution of metal oxide in CA/TiO2 nanocomposites was achieved on grafted acrylic acid/chitosan which contains a weak anionic group (-COOH) using ultrasonication technique. Physiochemical techniques such as X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), Fourier Transform Infra-Red spectroscopy (FT-IR), Energy Dispersive X-ray spectroscopy (EDX), and Thermal Gravimetric Analysis (TGA) were employed to characterize synthesized CAT. Nanocomposite CAT was applied for degradation of industrial dye. Malachite green (MG) often presents in the waste waters. The degradation kinetics were studied by monitoring the photocatalytic reaction for degradation of MG under visible light, and the rate constant of the reaction was found to be 7.13x10−3min−1. The current research work opens vistas for the new dimensions in the area of water treatment by solving the issues related to degradation reaction efficiency in visible light and cost effectiveness.