Efficient photodecomposition of herbicide imazapyr over mesoporous Ga2O3-TiO2 nanocomposites

The state-of-the-art development of photocatalysts for the degradation of persistent herbicides in wastewater

Herbicides are one of the most recurring pollutants in the aquatic system due to their widespread usage in the agriculture sector for weed control. Semiconductor-based photocatalysts have gained recognition due to their ability to degrade and mineralize pollutants into harmless by-products completely. Lately, many studies have been done to design photocatalysts with efficient separation of photogenerated charge carriers and enhanced light absorption. Photocatalyst engineering through doping with metal and non-metal elements and the formation of heterojunction are proven effective for minimizing the recombination of electron-hole pairs and enlarging the absorption in the visible light region. This review focuses on discussing and evaluating the recent progress in the types of photocatalysts and their performance in the remediation of herbicides in wastewater. The development of innovative hybrid technologies is also highlighted. The limitations and challenges of photocatalysis technology in the present literature have been identified, and future studies are recommended.

Visible-light responsive ZnSe-anchored mesoporous TiO2heterostructures for boosted photocatalytic reduction of Cr(VI)

The accumulation of Cr(VI) ions in water can cause serious influences on the environment and human health. This work reports a humble synthesis of ZnSe nanoparticles anchored to the sol-gel prepared TiO₂for visible-light-driven photocatalytic reduction of Cr(VI) ions. The 7.9 nm ZnSe nanoparticles were attached to TiO₂surfaces at a content of 1.0-4.0 wt% as experiential by TEM investigation. The designed nanocomposite unveiled mesostructured surfaces exhibiting surface areas of 176-210 m²g^-1. The impregnation of ZnSe amended the visible-light absorption of TiO₂due to the bandgap decrease from 3.14 to 2.90 eV. The photocatalytic reduction of Cr(VI) applying the optimized portion of 3.0 wt% ZnSe/TiO₂was achieved at 177μmol min^-1. This photocatalytic activity is higher than the common Degussa P25 and pristine TiO₂by 20 and 30 times, respectively. The improved performance is signified by the efficient interfacial separation of charge carriers by the introduction of ZnSe. This innovative ZnSe/TiO₂has also shown photocatalytic stability for five consecutive runs.

Design and Preparation of Biomass-Derived Activated Carbon Loaded TiO2 Photocatalyst for Photocatalytic Degradation of Reactive Red 120 and Ofloxacin

The design and development of novel photocatalysts for treating toxic substances such as industrial waste, dyes, pesticides, and pharmaceutical wastes remain a challenging task even today. To this end, a biowaste pistachio-shell-derived activated carbon (AC) loaded TiO₂ (AC-TiO₂) nanocomposite was fabricated and effectively utilized towards the photocatalytic degradation of toxic azo dye Reactive Red 120 (RR 120) and ofloxacin (OFL) under UV-A light. The synthesized materials were characterized for their structural and surface morphology features through various spectroscopic and microscopic techniques, including high-resolution transmission electron microscope (HR-TEM), field emission scanning electron microscope (FE-SEM) along with energy dispersive spectra (EDS), diffuse reflectance spectra (DRS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, photoluminescence spectra (PL) and BET surface area measurements. AC-TiO₂ shows enhanced photocatalytic activity compared to bare TiO₂ due to the change in the bandgap energy and effective charge separation. The degradation rate of dyes was affected by the bandgap of the semiconductor, which was the result of the deposition weight percentage of AC onto the TiO₂. The presence of AC influences the photocatalytic activity of AC-TiO₂ composite towards RR 120 and OFL degradation. The presence of heteroatoms-enriched AC enhances the charge mobility and suppresses the electron-hole recombination in AC-TiO₂ composite, which enhances the photocatalytic activity of the composite. The hybrid material AC-TiO₂ composite displayed a higher photocatalytic activity against Reactive Red 120 and ofloxacin. The stability of the AC-TiO₂ was tested against RR 120 dye degradation with multiple runs. GC-MS analyzed the degradation intermediates, and a suitable degradation pathway was also proposed. These results demonstrate that AC-TiO₂ composite could be effectively used as an ecofriendly, cost-effective, stable, and highly efficient photocatalyst.

Porous Ga2 O3 Nanotubes Derived from Urease-Mediated Interfacially-Grown NH4 Ga(OH)2 CO3 for High-Efficient Hydrogen Evolution

The authors proposed a novel template-free strategy, urease-mediated interfacial growth of NH₄ Ga(OH)₂ CO₃ nanotubes at 20-50 °C, to fabricate the porous Ga₂ O₃ nanotubes. The subtlety of the proposed strategy is all the products from urea enzymolysis are utilized in formation of NH₄ Ga(OH)₂ CO₃ precipitates, and the key for interfacial growth of NH₄ Ga(OH)₂ CO₃ nanotubes is the dynamic match between the rate of CO₂ bubble fusion and NH₄ Ga(OH)₂ CO₃ precipitation. The proposed strategy works well for the doped porous Ga₂ O₃ nanotubes. As a proof-of-concept, the porous β-Ga₂ O₃ and β-Ga₂ O₃ :Cr_0.001 nanotubes are used as photocatalysts or co-catalysts with Pt, for H₂ evolution from water splitting. The H₂ evolution rate of porous β-Ga₂ O₃ nanotubes reach 39.3 mmol g^-1 h^-1 with solar-to-hydrogen (STH) conversion efficiency of 2.11% (Hg lamp) or 498 µmol g^-1 h^-1 with STH of 0.03% (Xe lamp) respectively, both about 3 times of β-Ga₂ O₃ nanoparticles synthesized at pH 9.0 without urease. The Cr-doping enhances the in-the-dark H₂ evolution rate pre-lighted by Hg lamp, and Pt co-catalysis further elevates the H₂ evolution rate, for instance, the H₂ evolution rate of Pt-loaded β-Ga₂ O₃ :Cr_0.001 nanotubes reaches 54.7 mmol g^-1 h^-1 with STH of 2.94% under continuous lighting of Hg lamp and 1062 µmol g^-1 h^-1 in-the-dark.

A Review on Metal Ions Modified TiO2 for Photocatalytic Degradation of Organic Pollutants

TiO2 is a semiconductor material with high chemical stability and low toxicity. It is widely used in the fields of catalysis, sensing, hydrogen production, optics and optoelectronics. However, TiO2 photocatalyst is sensitive to ultraviolet (UV) light; this is why its photocatalytic activity and quantum efficiency are reduced. To enhance the photocatalytic efficiency in the visible light range as well as to increase the number of the active sites on the crystal surface or inhibit the recombination rate of photogenerated electron–hole pairs electrons, various metal ions were used to modify TiO2. This review paper comprehensively summarizes the latest progress on the modification of TiO2 photocatalyst by a variety of metal ions. Lastly, the future prospects of the modification of TiO2 as a photocatalyst are proposed.

Visible light photocatalytic properties of one-step SnO2-templated grown SnO2/SnS2heterostructure and SnS2nanoflakes

The nanoflakes of SnS₂/SnO₂heterostructure and SnS₂were synthesized by a one-step SnO₂-templated chemical vapor deposition method. The metal oxide-assisted growth mechanism of SnS₂/SnO₂heterostructure and SnS₂nanoflakes were realized through investigating serial microstructures of products with varied growth time. Furthermore, the photocatalytic activity for MB dyes degradation of varied growth time products was used to explore the effect of product microstructure under the visible light irradiation. The SnO₂/SnS₂heterostructure and the oxide vacancies of nanoflakes demonstrated an improved visible light photocatalytic performance for MB degradation, which was around twice of the pure SnS₂nanoflakes and better than P25. The results of different scavengers on the degradation efficiency for MB indicate the·O₂^-, and ·OH are the main active species in the photodegradation reaction. The one-step growth mechanism of SnS₂/SnO₂could prove a facile process to grow metal oxide-metal sulfide heterostructure.

Green sonochemical synthesis of BaDy2NiO5/Dy2O3 and BaDy2NiO5/NiO nanocomposites in the presence of core almond as a capping agent and their application as photocatalysts for the removal of organic dyes in water

The present work reports the sonochemical synthesis of DBNO NC (dysprosium nickelate nanocomposite) using metal nitrates and core almond as a capping agent. In addition, the effects of the power of ultrasound irradiation were investigated. The BaDy2NiO5/Dy2O3 and BaDy2NiO5/NiO nanocomposites were synthesized with sonication powers of 50 and 30 W, respectively. The agglomerated nanoparticles were obtained using different sonication powers, including 15, 30, and 50 W. The results showed that upon increasing the sonication power, the particle size decreased. After characterization, the optical, electrical, magnetic, and photocatalytic properties of the NC were studied. The nanocomposites showed an antiferromagnetic behavior. In this study, the photocatalytic degradations of two dyes, AR14 and AB92, were investigated in the presence of DBNO NC. Furthermore, the effects of the amount of photocatalyst, the concentration of the dye solution, the type of organic dye, and light irradiation on the photocatalytic activity of the nanocomposite were studied. The results showed that with an increasing amount of catalyst and decreasing concentration of dye, the photocatalytic activity of the nanocomposite was increased. This activity for the degradation of AR14 is higher than that of AB92. Both AR14 and AB92 dyes show higher photocatalytic degradation under UV irradiation than under Vis irradiation.

Improving the Imazapyr Degradation by Photocatalytic Ozonation: A Comparative Study with Different Oxidative Chemical Processes

The degradation of imazapyr (C13H15N3O3), an active element in the aqueous solution of commercial herbicide, was investigated. This study was the first to evaluate in a comprehensive manner the efficiency of advanced oxidation processes for imazapyr degradation. Results showed that Imazapyr degradation is significantly affected by operational conditions such as TiO2 concentration, ozone concentration, initial concentration of imazapyr and pH. The kinetics of Imazapyr consumption was the first order with respect to Imazapyr concentration and zero order with respect to ozone concentration with a constant rate of 0.247 min−1 and 0.128 min−1 for photocatalytic ozonation and heterogeneous photocatalysis, while it was the first order with respect to Imazapyr and the first order with respect to ozone concentrations when only ozone was used with a constant rate of 0.053 mol L−1 min−1 at pH 7. The results revealed that more than 90 percent of the removal efficiency representing the elimination of imazapyr was held up to 7 μM. Further increase in the concentration of imazapyr leads to a drop in the removal efficiency, however the total imazapyr degradation was reached in 20 min utilizing photocatalytic ozonation for 5 μM of Imazapyr in the presence of 100 mg L−1 of TiO2, 10 mg L−1 of ozone at pH 7. Photocatalytic ozonation and heterogeneous photocatalysis utilizing TiO2 as a semiconductor process appeared possible and well suited for the treatment of organic contaminants such as imazapyr herbicides, although at certain dosages of pH and common time for wastewater treatment, imazapyr was not degraded with ozonation on its own. The association of two oxidation processes, ozonation and photocatalysis, has improved oxidation efficiencies for water treatment under optimal conditions, leading to the development of non-selective hydroxyl and more reactive radicals in the oxidation medium, as well as the resulting synergistic effects between photocatalysis and ozonation that react more rapidly with imazapyr herbicide.

Porous nickel doped titanium dioxide nanoparticles with improved visible light photocatalytic activity

A green hydrothermal synthesis route to prepare a porous nickel doped titanium dioxide (Ni-TiO₂) nanostructured photocatalyst has been developed in this research. The results show that Ni doping can greatly increase the visible light photocatalytic performance of TiO₂ through the introduction of impurity bands in the band gap of TiO₂. After 5 cycles of reuse, Ni-TiO₂ nanoparticles still show stable photocatalytic activity for MB degradation. The Ni-TiO₂ nanoparticles developed in the present study are expected to have great potential applications in wastewater treatment due to the advantages of strong visible light photocatalytic performance, a simple synthetic process and high cycle utilization performance.

Phase junction enhanced photocatalytic activity of Ga2O3 nanorod arrays on flexible glass fiber fabric

Ga₂O₃ nanostructures hold great potential applications in photocatalytic fields due to their stability, high efficiency and environmental friendliness. The construction of phase junction has been proved to be one of the most effective strategies for enhancing Ga₂O₃ photocatalytic activity. However, the influence of the formation process at the interface of the phase junction on the photocatalytic activity of Ga₂O₃ nanostructures is far less well understood. In this work, for the first time, large-area Ga₂O₃ nanorod arrays (NRAs) with controllable α/β phase junction were prepared in situ on a flexible glass fiber fabric by a facile and environmentally friendly three-step method. The α/β-Ga₂O₃ phase junction NRAs exhibit an ultra-high photocatalytic degradation rate of 97% during Ultraviolet (UV) irradiation for 60 min, which is attributed to a unique phase junction promoting efficient charge separation. However, the photocatalytic activity of α/β-Ga₂O₃ phase junction NRAs is not evident in the early phase transition, possibly due to the presence of defects acting as charge recombination centers.

Ga₂O₃ nanostructures hold great potential applications in photocatalytic fields due to their stability, high efficiency and environmental friendliness.

Photocatalytic degradation of tetracycline hydrochloride over rugby-like β-Ga2O3 with a 3D hierarchically assembled porous structure for environmental remediation

A novel rugby ball-like β-Ga₂O₃ photocatalyst with a 3D hierarchically assembled porous structure was constructed via a facile precipitation–calcination method. The as-synthesized Ga₂O₃ exhibits a high photocatalytic efficiency compared to commercial Ga₂O₃ and Degussa P25.

Evaluation of photoassisted treatments for norfloxacin removal in water using mesoporous Fe2O3-TiO2 materials

We report the synthesis of mesoporous TiO₂ and mesoporous Fe₂O₃-TiO₂ catalysts by using a structure-directing-surfactant method, their characterization and their employment as photocatalysts for norfloxacin degradation in aqueous solution. The main findings show that in the presence of both O₂ and H₂O₂, Fe-containing mesoporous titania (Fe₂O₃-TiO₂), with iron percentages between 1 and 3 wt%, exhibited norfloxacin degradation rates more than 60% greater than otherwise identical mesoporous titania without iron. Furthermore, the activity of the mesoporous composite catalysts also exceeds that of titania when illuminated with 405 nm light-emitting diodes. Iron loading improved the photocatalytic activity for norfloxacin degradation with values of apparent reaction rate constants of 0.037 min^-1 and 0.076 min^-1 with 1 and 3 surface wt.% of iron, respectively. An optimum of activity was found with the 3 wt% Fe₂O₃-TiO₂ catalyst. Under these conditions, 10 mg/L of norfloxacin is reacted essentially to completion and 90% of total organic carbon conversion was obtained within 120 min of reaction. This higher organic carbon conversion degree was reached due to the photo-oxidation of short-chain organic acids. The high activity of the as-synthesized mesoporous composites is attributed to the additional iron phase which led to the different reactions for H₂O₂ decomposition, but also due to the improvement in light absorbance. Finally, the activity of the most active catalyst was found to be stable over multiple sequential runs, which was related to a negligible amount of iron leaching (<0.1%) from these materials.

Wafer-Scale Fabrication of Sub-10 nm TiO2-Ga2O3 n-p Heterojunctions with Efficient Photocatalytic Activity by Atomic Layer Deposition

Wafer-scale, conformal, two-dimensional (2D) TiO₂-Ga₂O₃ n-p heterostructures with a thickness of less than 10 nm were fabricated on the Si/SiO₂ substrates by the atomic layer deposition (ALD) technique for the first time with subsequent post-deposition annealing at a temperature of 250 °C. The best deposition parameters were established. The structure and morphology of 2D TiO₂-Ga₂O₃ n-p heterostructures were characterized by the scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), etc. 2D TiO₂-Ga₂O₃ n-p heterostructures demonstrated efficient photocatalytic activity towards methyl orange (MO) degradation at the UV light (λ = 254 nm) irradiation. The improvement of TiO₂-Ga₂O₃ n-p heterostructure capabilities is due to the development of the defects on Ga₂O₃-TiO₂ interface, which were able to trap electrons faster.

Ferroelectric Oxide Nanocomposites with Trimodal Pore Structure for High Photocatalytic Performance

An effective method to improve the photocatalytic performances of powder catalysts is to use the internal electric field from ferroelectrics to separate photogenerated charge carriers. The design and engineering of a complex hetero-junction with a hierarchical pore structure is highly desirable for the efficient application of ferroelectric materials in photocatalysis. Here, we present a novel strategy using two templates to fabricate PbTiO₃/TiO₂/carbon (PTC) nanocomposites with a tunable microstructure. A hard SiO₂ template combined with an ice template followed by an appropriate pyrolysis procedure introduced trimodal (micro-, meso-, macro-) porosity. The as-prepared PTC nanocomposites with optimal mass ratio exhibited excellent photocatalytic and photoelectrochemical performances. PbTiO₃/TiO₂ annealed at 900 °C (PTC-900) showed a MB degradation rate of 0.21 and 0.021 min^-1 under UV and visible light irradiation, which are, respectively, 7.2 and 3 times those of pure PbTiO₃. The photocurrent density of the composite catalyst is 1.48 mA cm^-2 at the potential of 1.0 V versus saturated calomel electrode, and the rates of hydrogen generation of PTC-900 are as high as 2360 and 9.6 μmol h^-1 g^-1 under UV and visible light irradiation, respectively. More importantly, the simultaneous application of ultrasound-induced mechanical waves further improved the photocatalytic reactivity. This work serves to improve understanding on the design of ferroelectric/piezoelectric photocatalysts with a hierarchical pore structure and also proposes a widely applicable strategy for the fabrication of high-performance micro-nano/nano-nano structures.

Nanostructured Oxides Containing Ga: Materials with Unique Properties for Aqueous-Based Applications

Oxides containing Ga have been studied by various research communities due to their stability under harsh conditions as well as conductivity and luminescence properties. Nanostructured forms of such oxides can be fabricated by a variety of methods. Advances in synthesis approaches have focused on control over size and shape that can permit adaptation in applied interfaces related to medicine, energy, and the environment. Chemical functionalization can enhance the stability of nanostructured oxides containing Ga in aqueous solutions. In this prospective, we summarize progress in making these materials as well as functionalizing them in water solutions. The prospective also identifies future opportunities with these materials in applied and fundamental materials chemistry research.