A mechanistic study of the photocatalytic activity of AgI–WO3 in an experimentally designed approach toward methylene blue photodegradation

The visible light-active AgI/WO3 binary photocatalyst has been characterized using XRD, FTIR spectroscopy, SEM-EDX, cyclic voltammetry (CV), photoluminescence (PL), and UV–vis DRS techniques.

A Cyclen-Functionalized Cobalt-Substituted Sandwich-Type Tungstoarsenate with Versatility in Removal of Methylene Blue and Anti-ROS-Sensitive Tumor Cells

Oxidative degradation by using reactive oxygen species (ROS) is an effective method to treat pollutants. The synthesis of artificial oxidase for the degradation of dyes is a hot spot in molecular science. In this study, a nanoscale sandwich-type polyoxometalate (POM) on the basis of a tetra-nuclear cobalt cluster and trivacant B-α-Keggin-type tungstoarsenate {[Co(C₈H₂₀N₄)]₄}{Co₄(H₂O)₂[HAsW₉O₃₄]₂}∙4H₂O (abbreviated as CAW, C₈H₂₀N₄ = cyclen) has been synthesized and structurally examined by infrared (IR) spectrum, ultraviolet–visible (UV–Vis) spectrum, X-ray photoelectron spectrum (XPS), single-crystal X-ray diffraction (SXRD), and bond valence sum (Σs) calculation. According to the structural analysis, the principal element of the CAW is derived from modifying sandwich-type polyanion {Co₄(H₂O)₂ [HAsW₉O₃₄]₂}^8– with four [Co(Cyclen)]²⁺, in which 1,4,7,10-tetraazacyclododecane (cyclen) is firstly applied to modify POM. It is also demonstrated that CAW is capable of efficiently catalyzing the production of ROS by the synergistic effects of POM fragments and Co–cyclen complexes. Moreover, CAW can interfere with the morphology and proliferation of sensitive cells by producing ROS and exhibits ability in specifically eliminating methylene blue (MB) dyes from the solution system by both adsorption and catalytic oxidation.

Hydrothermal Synthesis of K2Ti6O13 Nanotubes/Nanoparticles: A Photodegradation Study on Methylene Blue and Rhodamine B Dyes

The degradation of methylene blue and rhodamine B dyes using potassium hexatitanate nanoparticles (KTNPs) and potassium hexatitanate nanotubes (KTNTs) synthesized via a hydrothermal method as efficient photocatalysts under UV light irradiation was investigated. The kinetics of degradation was determined for the two different catalysts--KTNPs and KTNTs--by monitoring the optical absorption of the dyes. The as-synthesized KTNPs were found to be spherical in shape with an average particle size of ∼36 ± 1.7 nm, whereas the KTNTs evidenced a tubular hollow structure with ∼7 nm internal diameter and ∼12 nm external diameter, as perused by structural and morphological studies. The larger surface area of KTNTs showed a greater impact on the photodegradation of dyes manifesting their high potential as compared to KTNPs under UV irradiation, and the reusability studies showed more than 90% (KTNTs) and 80% (KTNPs) degradation of the dyes even after the fourth cycle elucidating their stability.

Highly crystalline Na0.5Bi0.5TiO3 of a photocatalyst valence-band-controlled with Bi(III) for solar water splitting

Na0.5Bi0.5TiO3 (BG 3.1 eV) with a valence band formed by Bi(iii) was found as a new photocatalyst for solar water splitting. The water splitting activity of highly crystalline Na0.5Bi0.5TiO3 synthesized by a flux method was much higher than that of the samples synthesized by a solid-state reaction. The optimized RhCr2Ox(0.1 mol%)/Na0.5Bi0.5TiO3/CoOOH(0.02 mol%) gave a 5.1% apparent quantum yield at 350 nm and split water even under simulated sunlight irradiation with a 0.05% solar to hydrogen energy conversion efficiency. We have successfully achieved solar water splitting using a one-step photoexcitation type photocatalyst valence-band-controlled with Bi(iii).

Efficient urine removal, simultaneous elimination of emerging contaminants, and control of toxic chlorate in a photoelectrocatalytic-chlorine system

Urine, which is an important waste biomass resource, is the main source of nitrogen in sewage and contains large quantities of emerging contaminants (ECs). In this study, we propose a new method to efficiently remove urine, simultaneously eliminate ECs, and control the generation of toxic chlorate during urine treatment using a photoelectrocatalytic-chlorine (PEC-Cl) system. A type-II heterojunction of WO₃/BiVO₄ was used as a photoanode to generate chlorine radicals (Cl•) by decreasing the oxidation potential of WO₃ valence band for the highly selective conversion of urine to N₂ and the simultaneous degradation of ECs in an efficient manner. The method presented surprising results. It was observed that the amount of toxic chlorate was significantly inhibited by circumventing the over-oxidation of Cl^- by holes or hydroxyl radicals (•OH). Moreover, the removal of urea nitrogen reached 97% within 90 min, while the degradation rate of trimethoprim in urine was above 98.6% within 60 min, which was eight times more than that in the PEC system (12.1%). Compared to the bare WO₃ photoanode, the toxic chlorate and nitrate generated by the WO₃/BiVO₄ heterojunction photoanode decreased by 61% and 44%, respectively. Thus, this study provides a safe, efficient, and environmentally-friendly approach for the disposal of urine.

In-situ growth of high-density ultrafine Ag3PO4 nanoparticles on 3D TiO2 hierarchical spheres for enhanced photocatalytic degradation of organic pollutants

Silver phosphate (Ag₃PO₄, APO) has attracted intense attention as a visible-light-driven photocatalyst, but its large-scale application is limited by severe charge recombination and inevitable photo-corrosion. Various rational APO-based heterostructures composed of APO nanoparticles (NPs) and band-matched semiconductor support are designed to address the above issues. Nevertheless, the size, density, stability, and dispersion of APO NPs are critical challenges for the photocatalytic performance of APO-based photocatalysts. Here, three-dimensional (3D) self-assembled TiO₂ hierarchical spheres (THS) prepared by a simple one-step hydrothermal method are employed as innovative support, and ultrafine high-density APO NPs with an average size of about 3 nm are successfully deposited and uniformly dispersed throughout THS to form hierarchical THS/APO composites. The novel THS/APO microstructure provides abundant reactive sites for photocatalytic reactions and promotes the photogenerated charge separation and transfer due to the ultrafine size of APO NPs and the TiO₂/APO Type-II heterojunction. As a result, the THS/APO composites show significant improvement in photocatalytic activity and stability in methylene blue (MB) degradation. The reaction constant of THS/APO composites far exceeds that of either THS or APO, roughly 16 and 7 times higher than that of THS and APO under full-spectrum light, and 41 and 4 times higher under visible light. Our results strongly suggest new insights into the low-cost, large-scale application of high-efficiency APO-based photocatalyst.

Facile Formation of Anatase Nanoparticles on H-Titanate Nanotubes at Low Temperature for Efficient Visible Light-Driven Degradation of Organic Pollutants

Anatase nanoparticles (5–10 nm) generated on H-titanate nanotube surface (H-titanate/anatase) were prepared by an ingenious and simple method. H-titanate tubes were prepared by a hydrothermal reaction of Ti powder in concentrated NaOH solution and an ion exchange process with HNO3 solution. After that, at a relatively low drying temperature (100 °C), a small quantity of anatase nanoparticles were in-situ formed on the H-titanate tubes surface by a surface dehydration reaction. In-situ transformation can form a strong interface coupling between H-titanate and anatase, which is conducive to accelerating charge transfer and improving its photocatalytic activity. In addition, the smaller average crystal size, the large specific surface areas (BET), the nanotubed and layered structure and the synergistic effect of dual phases would be beneficial to improving the photocatalytic efficiency.

Green Fabrication of Tannic Acid-Inspired Magnetic Composite Nanoparticles toward Cationic Dye Capture and Selective Degradation

An environmental strategy for developing sustainable materials presents an attractive prospect for wastewater remediation. Herein, a facile, green, and economical strategy is proposed to fabricate magnetic composite nanoparticles (NPs) toward cationic dye adsorption and selective degradation. To prepare the composite TiO2-PEI-TA@Fe3O4 NPs, tannic acid (TA) and polyethyleneimine (PEI) were first used to decorate Fe3O4 NPs at aqueous solution, and then TiO2 NPs were anchored onto the surfaces of Fe3O4 NPs based on the catecholamine chemistry. The chemical composition and microstructure of the obtained NPs were systematically characterized. The NPs not only exhibited adsorption ability for the cationic dye of methylene blue (MB) but also responded to ultraviolet light to selectively degrade the adsorbed MB, and the removal (adsorption and/or degradation) ratio for MB could reach 95%. In addition, cyclic experiments showed that the removal ratio of the composite NPs for MB could still be maintained more than 85% even after five cycles. Given by the above-mentioned advantages, such a green and facile strategy for combining the adsorption and degradation methods to construct magnetic nanocomposites exhibits potential applications in cationic dye selective removal and sustainable wastewater remediation.

2D MXene-derived Nb2O5/C/Nb2C/g-C3N4 heterojunctions for efficient nitrogen photofixation

Novel 2D MXene-derived Nb₂O₅/C/Nb₂C/g-C₃N₄ showed a high nitrogen reduction rate in water (0.365 mmol h⁻¹ g_cat⁻¹); the nitrogen reduction efficiency could be further promoted 2.5 times (0.927 mmol h⁻¹ g_cat⁻¹) with the optimized pH of 9.

Flux synthesis of Ba2Li2/3Ti16/3O13 and its photocatalytic performance

Barium-lithium titanate (Ba₂Li_2/3Ti_16/3O₁₃) was synthesized by using a flux method under some conditions with various chloride salts as the flux, thermal treatment temperatures, solute concentrations, and cooling rates. As a result, fine particles of this material with a rod-like morphology were obtained for the first time. It is suggested that this morphology with high crystallinity is responsible for the increase in the photocatalytic activity of this material without any co-catalyst for H₂ and CO evolution from water and CO₂. The observed photocatalytic performance is discussed taking into consideration the differences in physicochemical properties, obtained as a result of the synthesis using this method under the different conditions.

PG-PEI-Ag NPs-Decorated Membrane for Pretreatment of Laboratory Wastewater: Simultaneous Removal of Water-Insoluble Organic Solvents and Water-Soluble Anionic Organic Pollutants

Generally, waste liquid in laboratory can be roughly classified into organic wastewater and inorganic wastewater. However, in some experiments, organic phase and water phase are inevitably mixed together, leaving the postclassification and disposal intractable. Traditionally, we used methods like distillation and extraction to separate these two phases, however, always consuming significant amounts of labor and time and meanwhile having an unsatisfactory separation efficiency. Here, we proposed an improved processing method with a propyl gallate (PG)-polyethyleneimine (PEI)-Ag nanoparticles (NPs)-decorated membrane, possessing the special wettability designed for organic and water phase separation. Accordingly, various kinds of organic solvents/water mixtures were tested, where the PG-PEI-Ag NPs-decorated membrane was used like a common filter paper, fixed onto the funnel of the waste liquid barrel. Afterward, the two phase mixtures were poured onto the membrane; as a result, the organic phase was blocked above while the water phase was left below. All kinds of organic solvents/water mixtures showed higher than 99.90% removal efficiency. Besides, the membrane can remove water-soluble anionic organic molecules through electrostatic interaction. Thus, along the phase separation, anionic organic molecules in water can be removed simultaneously. This pretreatment of lab wastewater with the PG-PEI-Ag NPs-decorated membrane is simple and efficient, relieving the pressure of postcollection and disposal to some extent.

Unique 1D/3D K2Ti6O13/TiO2 micro-nano heteroarchitectures: controlled hydrothermal crystal growth and enhanced photocatalytic performance for water purification

Unique 1D/3D K₂Ti₆O₁₃/TiO₂ micro-nano heteroarchitectures with enhanced photocatalytic performance for pollutant degradation were successfully fabricated through a controlled hydrothermal route.