Effect of electron acceptors H2O2 and O2 on the generated reactive oxygen species 1O2 and OH in TiO2-catalyzed photocatalytic oxidation of glycerol

Selective oxidation of glycerol mediated by surface plasmon of gold nanoparticles deposited on titanium dioxide nanowires

This paper describes an alternative method for the in situ synthesis of gold nanoparticles (AuNPs) with a particle size of less than 3 nm, using nanoreactors formed by reverse micelles of 1,4-bis-(2-ethylhexyl) sulfosuccinate sodium (AOT) and nanoparticle stabilization with l-cysteine, which favor the preparation of nanoparticles with size and shape control, which are homogeneously dispersed (1% by weight) on the support of titanium dioxide nanowires (TNWs). To study the activity and selectivity of the prepared catalyst (AuNPs@TNWs), an aqueous solution of 40 mM glycerol was irradiated with a green laser (λ = 530 nm, power = 100 mW) in the presence of the catalyst and O2 as an oxidant at 22 °C for 6 h, obtaining a glycerol conversion of 86% with a selectivity towards hydroxypyruvic acid (HA) of more than 90%. From the control and reactions, we concluded that the Ti-OH groups promote the glycerol adsorption on the nanowires surface and the surface plasmon of the gold nanoparticles favors the selectivity of the reaction towards the hydroxypyruvic acid.

Selective Photoelectrochemical Oxidation of Glycerol to Glyceric Acid on (002) Facets Exposed WO3 Nanosheets

Glycerol is a byproduct of biodiesel production. Selective photoelectrochemical oxidation of glycerol to high value-added chemicals offers an economical and sustainable approach to transform renewable feedstock as well as store green energy at the same time. In this work, we synthesized monoclinic WO3 nanosheets with exposed (002) facets, which could selectively oxidize glycerol to glyceric acid (GLYA) with a photocurrent density of 1.7 mA cm-2 , a 73 % GLYA selectivity and a 39 % GLYA Faradaic efficiency at 0.9 V vs. reversible hydrogen electrode (RHE) under AM 1.5G illumination (100 mW cm-2 ). Compared to (200) facets exposed WO3 , a combination of experiments and theoretical calculations indicates that the superior performance of selective glycerol oxidation mainly originates from the better charge separation and prolonged carrier lifetime resulted from the plenty of surface trapping states, lower energy barrier of the glycerol-to-GLYA reaction pathway, more abundant active sites and stronger oxidative ability of photogenerated holes on the (002) facets exposed WO3 . Our findings show great potential to significantly contribute to the sustainable and environmentally friendly chemical processes via designing high performance photoelectrochemical cell via facet engineering for renewable feedstock transformation.

A Review on Nano Ti-Based Oxides for Dark and Photocatalysis: From Photoinduced Processes to Bioimplant Applications

Catalysis on TiO₂ nanomaterials in the presence of H₂O and oxygen plays a crucial role in the advancement of many different fields, such as clean energy technologies, catalysis, disinfection, and bioimplants. Photocatalysis on TiO₂ nanomaterials is well-established and has advanced in the last decades in terms of the understanding of its underlying principles and improvement of its efficiency. Meanwhile, the increasing complexity of modern scientific challenges in disinfection and bioimplants requires a profound mechanistic understanding of both residual and dark catalysis. Here, an overview of the progress made in TiO₂ catalysis is given both in the presence and absence of light. It begins with the mechanisms involving reactive oxygen species (ROS) in TiO₂ photocatalysis. This is followed by improvements in their photocatalytic efficiency due to their nanomorphology and states by enhancing charge separation and increasing light harvesting. A subsection on black TiO₂ nanomaterials and their interesting properties and physics is also included. Progress in residual catalysis and dark catalysis on TiO₂ are then presented. Safety, microbicidal effect, and studies on Ti-oxides for bioimplants are also presented. Finally, conclusions and future perspectives in light of disinfection and bioimplant application are given.

Selective Oxidation of Glycerol into Formic Acid by Photogenerated Holes and Superoxide Radicals

Photocatalysis is a promising technology for conversion of the glycerol into formic acid, but photocatalytic oxidation of C-C bonds in glycerol exhibits poor selectivity towards formic acid because the photogenerated radicals (e.g., hydroxyl radicals) further oxidize formic acid to CO₂ . In this work, a synergy of photogenerated holes and superoxide radicals that achieved the selective oxidation of glycerol into formic acid over the TiO₂ catalyst was revealed. The charge separation of pristine TiO₂ was improved with the aid of oxygen, which resulted in efficient hole oxidation of the C-C bonds in glycerol to formic acid. Surface active species were controlled to prevent being converted to hydroxyl radicals on TiO₂ by controlling the oxygen and water contents, which solved the problem of formic acid peroxidation without sophisticated catalyst modifications. Mechanism studies suggested that glyceraldehyde and glycolaldehyde were the intermediates to generate formic acid. This work provides a green and efficient approach to produce formic acid as a liquid hydrogen carrier from bio-based alcohols.

Construction of core-shell Fe3O4@GO-CoPc photo-Fenton catalyst for superior removal of tetracycline: The role of GO in promotion of H2O2 to •OH conversion

A novel core-shell structured Fe₃O₄@GO-CoPc magnetic catalyst, which is with magnetite (Fe₃O₄) as the core, graphene oxide (GO) as the interlayer and cobalt-phthalocyanine (CoPc) as the shell, was successfully prepared and used as a heterogeneous photo-Fenton catalyst for tetracycline (TC) degradation in this work. The core-shell structure of the catalyst was confirmed by XRD, FTIR, SEM and TEM. BET and magnetic hysteresis loops measurements indicated that Fe₃O₄@GO-CoPc catalyst owned large specific surface area and could be easily recovered under an external magnetic field. Meanwhile, the experimental results of TC degradation demonstrated that the photo-Fenton efficiency of Fe₃O₄@GO-CoPc was excellent. When the reaction time was 120 min, TC could be degraded almost completely in the photo-Fenton system with Fe₃O₄@GO-CoPc. The high photo-Fenton catalytic activity of Fe₃O₄@GO-CoPc could be resulted from the effective transfer of photo-generated electrons between CoPc and Fe₃O₄ by GO. Moreover, the main reaction species, •OH, O₂•-, ¹O₂ and h⁺, were verified by the analysis of active species in this system. Finally, the mechanism analyses and quantitative analysis results of active species indicated that the introduction of GO accelerated the cycle between Fe(II) and Fe(III) as well as improved the effective utilization of H₂O₂ (the efficiency of conversion of H₂O₂ to •OH).

Current developments and future trends in photocatalytic glycerol valorization: process analysis

Challenges and opportunities in photocatalytic glycerol valorization to hydrogen and value-added liquid products: process analysis and parametric study.

Organic Degradation Potential of Real Greywater Using TiO2-Based Advanced Oxidation Processes

In keeping with the circular economy approach, reclaiming greywater (GW) is considered a sustainable approach to local reuse of wastewater and a viable option to reduce household demand for freshwater. This study investigated the mineralization of total organic carbon (TOC) in GW using TiO2-based advanced oxidation processes (AOPs) in a custom-built stirred tank reactor. The combinations of H2O2, O3, and immobilized TiO2 under either dark or UVA irradiation conditions were systematically evaluated—namely TiO2/dark, O3/dark (ozonation), H2O2/dark (peroxidation), TiO2/UVA (photocatalysis), O3/UVA (Ozone photolysis), H2O2/UVA (photo-peroxidation), O3/TiO2/dark (catalytic ozonation), O3/TiO2/UVA (photocatalytic ozonation), H2O2/TiO2/dark, H2O2/TiO2/UVA, H2O2/O3/dark (peroxonation), H2O2/O3/UVA (photo-peroxonation), H2O2/O3/TiO2/dark (catalytic peroxonation), and H2O2/O3/TiO2/UVA (photocatalytic peroxonation). It was found that combining different treatment methods with UVA irradiation dramatically enhanced the organic mineralization efficiency. The optimum TiO2 loading in this study was observed to be 0.96 mg/cm2 with the highest TOC removal (54%) achieved using photocatalytic peroxonation under optimal conditions (0.96 mg TiO2/cm2, 25 mg O3/min, and 0.7 H2O2/O3 molar ratio). In peroxonation and photo-peroxonation, the optimal H2O2/O3 molar ratio was identified to be a critical efficiency parameter maximizing the production of reactive radical species. Increasing ozone flow rate or H2O2 dosage was observed to cause an efficiency inhibition effect. This lab-based study demonstrates the potential for combined TiO2-AOP treatments to significantly reduce the organic fraction of real GW, offering potential for the development of low-cost systems permitting safe GW reuse.

Recent Advances in Heterogeneous Photo-Driven Oxidation of Organic Molecules by Reactive Oxygen Species

The photo-driven oxidation of organic molecules into corresponding high-value-added products has become a promising method in chemical synthesis. This strategy can drive thermodynamically non-spontaneous reactions and achieve challenging thermocatalytic processes under ambient conditions. Reactive oxygen species (ROS) are not only significant intermediates for producing target products via photoinduced oxidation reactions but also contribute to the creation of sustainable chemical processes. Here, the latest advances in heterogeneous photo-driven oxidation reactions involving ROS are summarized. The major types of ROS and their generation are introduced, and the behaviors of various ROS involved in photo-driven processes are reviewed in terms of the formation of different bonds. Emphasis is placed on unraveling the reaction mechanisms of ROS and establishing strategies for their regulation, and the remaining challenges and perspectives are summarized and analyzed. This Review is expected to provide an in-depth understanding of the mechanisms of ROS involved in photo-driven oxidation processes as an important foundation for the design of efficient catalysts. Clarifying the role of ROS in oxidation reactions has important scientific significance for improving the atomic and energy efficiency of reactions in practical applications.

Photoinduced Glycerol Oxidation over Plasmonic Au and AuM (M = Pt, Pd and Bi) Nanoparticle-Decorated TiO₂ Photocatalysts

In this study, sol-immobilization was used to prepare gold nanoparticle (Au NP)-decorated titanium dioxide (TiO₂) photocatalysts at different Au weight % (wt. %) loading (Au_x/TiO₂, where x is the Au wt. %) and Au–M NP-decorated TiO₂ photocatalysts (Au₃M₃/TiO₂), where M is bismuth (Bi), platinum (Pt) or palladium (Pd) at 3 wt. %. The Au_x/TiO₂ photocatalysts exhibited a stronger visible light absorption than the parent TiO₂ due to the localized surface plasmon resonance effect. Increasing the Au content from 1 wt. % to 7 wt. % led to increased visible light absorption due to the increasing presence of defective structures that were capable of enhancing the photocatalytic activity of the as-prepared catalyst. The addition of Pt and Pd coupled with the Au₃/TiO₂ to form Au₃M₃/TiO₂ improved the photocatalytic activity of the Au₃/TiO₂ photocatalyst by maximizing their light-absorption property. The Au₃/TiO₂, Au₃Pt₃/TiO₂ and Au₃Pd₃/TiO₂ photocatalysts promoted the formation of glyceraldehyde from glycerol as the principle product, while Au₃Bi₃/TiO₂ facilitated glycolaldehyde formation as the major product. Among all the prepared photocatalysts, Au₃Pd₃/TiO₂ exhibited the highest photocatalytic activity with a 98.75% glycerol conversion at 24 h of reaction time.

Enhancement of nano titanium dioxide coatings by fullerene and polyhydroxy fullerene in the photocatalytic degradation of the herbicide mesotrione

The surface modification of commercial TiO₂ Hombikat (TiO₂) using nanoparticles of fullerene C₆₀ with tetrahydrofuran (THF-nC₆₀), as well as fullerenol C₆₀(OH)₂₄ nanoparticles (FNP) was investigated in this study. Characterization of THF-nC₆₀, FNP, TiO₂, TiO₂/THF-nC₆₀, and TiO₂/FNP was studied by using DES, ELS, TEM, SEM, DRS and BET measurements and their photoactivity has been examined on the mesotrione degradation under simulated sunlight. It was found that FNP in self-assembled nanocomposite TiO₂/FNP increased negatively charge, as well as catalytic surface of TiO₂. In addition, TiO₂/FNP exhibits a shift of band gap energy to lower values compared to TiO₂ and TiO₂/THF-nC₆₀. BET surface area has not showed significant differences among catalysts. Furthermore, it was found that the highest photoactivity was obtained for TiO₂/FNP system. Besides, influence of different concentrations of electron acceptors (H₂O₂ and KBrO₃), as well as scavengers on the kinetics of mesotrione removal in aqueous solution with/without TiO₂ and FNP under simulated sunlight was investigated. Namely, addition of mentioned electron acceptors has resulted in higher mesotrione degradation efficiency compared to O₂ alone. Besides, in the first period substrate degradation probably takes place via hydroxyl radicals and after 60 min of irradiation the reaction mechanism proceeds mainly via holes. The most efficient system for mesotrione degradation and mineralization were TiO₂/7 mM KBrO₃ and TiO₂/7 mM KBrO₃/40 μl FNP, respectively.