Oxidative desulfurization of refinery diesel pool fractions using LaVO4 photocatalyst

Advancements in TiO2-based photocatalysis for environmental remediation: Strategies for enhancing visible-light-driven activity

Researchers have focused on efficient techniques for degrading hazardous organic pollutants due to their negative impacts on ecological systems, necessitating immediate remediation. Specifically, TiO2-based photocatalysts, a wide-bandgap semiconductor material, have been extensively studied for their application in environmental remediation. However, the extensive band gap energy and speedy reattachment of electron (e-) and hole (h+) pairs in bare TiO2 are considered major disadvantages for photocatalysis. This review extensively focuses on the combination of semiconducting photocatalysts for commercial outcomes to develop efficient heterojunctions with high photocatalytic activity by minimizing the e-/h+ recombination rate. The improved activity of these heterojunctions is due to their greater surface area, rich active sites, narrow band gap, and high light-harvesting tendency. In this context, strategies for increasing visible light activity, including doping with metals and non-metals, surface modifications, morphology control, composite formation, heterojunction formation, bandgap engineering, surface plasmon resonance, and optimizing reaction conditions are discussed. Furthermore, this review critically assesses the latest developments in TiO2 photocatalysts for the efficient decomposition of various organic contaminants from wastewater, such as pharmaceutical waste, dyes, pesticides, aromatic hydrocarbons, and halo compounds. This review implies that doping is an effective, economical, and simple process for TiO2 nanostructures and that a heterogeneous photocatalytic mechanism is an eco-friendly substitute for the removal of various pollutants. This review provides valuable insights for researchers involved in the development of efficient photocatalysts for environmental remediation.

Low-temperature synthesis, characterization and photocatalytic properties of lanthanum vanadate LaVO4

In this study, we have successfully prepared tetragonal lanthanum vanadate LaVO₄ nanoparticles by a facile co-precipitation method at room temperature. The obtained materials were characterized using different structural and micro-structural techniques such as the characterization by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectrum (DRS), transmission electron microscopy (TEM), and Raman spectrometry. The obtained structure is crystallized in single tetragonal phase with pin-like nanostructure. A main optical transition with bandgap energy of 3.26 eV is evidenced, and the average lifetime of charges carriers was found to be 1 ns Furthermore, the photoluminescence occurs in the visible light range. The photocatalytic activity was evaluated by the photocatalytic degradation of methylene blue (MB) with initial concentration of 10 mg L^-1. The result indicates that LaVO₄ particles showed a best photocatalytic activity of 98.2% degradation for methylene blue solution after irradiation of 90 min under visible light. Furthermore, the photocatalytic mechanism and reusability were studied.

Studying the mechanism and kinetics of fuel desulfurization using CexOy/NiOx piezo-catalysts as a new low-temperature method

In order to advance desulfurization technology, a new method for excellent oxidative desulfurization of fuel at room temperature will be of paramount importance. As a novel desulfurization method, we developed piezo-catalysts that do not require adding any oxidants and can be performed at room temperature. A microwave method was used to prepare CeO₂/Ce₂O₃/NiO_x nanocomposites. Model and real fuel desulfurization rates were examined as a function of synthesis parameters, such as microwave power and time, and operation conditions, such as pH and ultrasonic power. The results showed that CeO₂/Ce₂O₃/NiO_x nanocomposites demonstrated outstanding piezo-desulfurization at room temperature for both model and real fuels. Furthermore, CeO₂/Ce₂O₃/NiO_x nanocomposites exhibited remarkable reusability, maintaining 79% of their piezo-catalytic activity even after 17 repetitions for desulfurization of real fuel. An investigation of the mechanism of sulfur oxidation revealed that superoxide radicals and holes played a major role. Additionally, the kinetic study revealed that sulfur removal by piezo-catalyst follows a second-order reaction kinetic model.

Mesoporous LaVO4/MCM-48 nanocomposite with visible-light-driven photocatalytic degradation of phenol in wastewater

Dearomatization through photocatalytic oxidation is a swiftly rising phenolic compounds removal technology that works at trifling operations requirements with a special emphasis on the generation of nontoxic products. The study aims to develop a LaVO₄/MCM-48 nanocomposite that was prepared via a hydrothermally approach assisting the employment of an MCM-48 matrix, which was then utilized for phenol degradation processes. Various techniques including UV-Vis DRS, FTIR, PL, Raman, TEM, and BET analyses are employed to characterize the developed photocatalyst. The developed photocatalyst presented remarkable characteristics, especially increased light photon utilization, and reduced recombination rate leading to enhanced visible-light-driven photodegradation performance owing to the improved specific surface area, specific porosities, and <2 eV narrow energy bandgap. The LaVO₄/MCM-48 nanocomposite was experienced on aqueous phenol solution having 20 mg/L concentration under visible-light exposure, demonstrating exceptional performance in photodegradation up to 99.28%, comparatively higher than pure LaVO₄. The conducted kinetic measurements revealed good accordance with pseudo first-order. A possible reaction mechanism for photocatalytic degradation was also predicted. The as-synthesized LaVO₄/MCM-48 nanocomposite presented excellent stability and recyclability.

Porous Ag3VO4/KIT-6 composite: Synthesis, characterization and enhanced photocatalytic performance for degradation of Congo Red

Novel Ag3VO4/KIT-6 nanocomposite photocatalyst has been successfully fabricated by a newly-designed simple hard-template induction process, in which the particles of Ag3VO4 were grown on the KIT-6 surface and inside the porous framework of the silica matrix. The developed porous framework nanocomposite was characterized by several techniques including N2-Physiosorption analysis. The obtained nanocomposite revealed a high surface area (273.86 m2/g) along with the possession of monoclinic Ag3VO4, which is highly responsive to visible light (with distinct intensity at about 700 nm). The UV-Vis DRS reveals that the Ag3VO4/KIT-6 photocatalyst bears a bandgap of 2.29 eV which confirms that the material has a good visible light response. The synthesized nanocomposite was tested for its superior physicochemical properties by evaluating its degradation efficiency for Congo Red (CR). The novel composite exhibited superior degradation capability of CR, reaching up to 96.49%, which was around three times the pure Ag3VO4. The detailed kinetic study revealed that the as-prepared material followed a pseudo first order kinetic model for the CR degradation. The study includes a comprehensive parametric study for the formulation of the optimized reaction conditions for photocatalytic reactions. The commercial applicability of the composite material was investigated by a regeneration and recyclability test, which revealed extraordinary results. Furthermore, the possible degradation pathway for CR was also proposed.

Catalytic Photodegradation of Cyclic Sulfur Compounds in a Model Fuel Using a Bench-scale Falling-film Reactor Irradiated by a Visible Light

A homemade N doped-TiO2 nanoparticle were used to degrade dibenzothiophene (DBT) in a model fuel flowing on a bench-scale glass-made falling film reactor irradiated by a xenon lamp that emitted visible light. The photocatalyst was immobilized on the glass sheet. EDS, SEM, and FT-IR techniques were utilized to identify the morphology of the N doped-TiO2 nanoparticles. Different operating parameters (e.g., N loading (0, 4, 5, and 6 wt%), light intensity (20, 40, and 60 W/m2), and pH (4, 7, and 10)) were investigated for their effect on the DBT degradation.  The effect of the N loading on the wettability of the nano-TiO2 particles was also investigated. Experimental results revealed that the N loading did not affect the wettability characteristics of the nano TiO2 particles. Moreover, results showed that DBT conversion positively depends on N loading, light intensity (hv), and pH increase. The estimated optimal operating parameters were 5 wt% N loading, pH = 10, and hv = 40 W/m2 to ensure the best photo-oxidation efficiency of 91.4% after 120 min of operation. The outcomes of the present work confirmed the effective efficiency of the N-doped TiO2 nanoparticles irradiated by visible light for DBT degradation. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Oxidative Desulfurization of Real High-Sulfur Diesel Using Dicarboxylic Acid/H2O2 System

From the perspective of pollution, economics, and product quality, it is very important to find an efficient way to minimize the sulfur content of petroleum products such as gasoline and diesel. In this work, an effective, inexpensive, and simple oxidative desulfurization system based on hydrogen peroxide activation by three dicarboxylic acids which have different carbon numbers (i.e., malonic acid, succinic acid, and glutaric acid) was utilized for the desulfurization of a real diesel sample with high organic sulfur-containing compounds. The desulfurization process was based on the oxidation of sulfur compounds in diesel fuel to the corresponding sulfones followed by acetonitrile extraction of the sulfones. To select the optimal experimental conditions, the effects of several parameters, including temperature, catalyst H2O2 dosages, and treatment time, were investigated. The results showed that the developed system was effective in desulfurizing real diesel fuel with high sulfur content. With an initial total sulfur content of about 8104 mg/L, the desulfurization rate from the diesel sample reached more than 90.9, 88.9, and 93%, using malonic acid, succinic acid, and glutaric acid, respectively. The optimum parameters such as reaction temperature, reaction time, H2O2 (50 w/w%), and carboxylic acid dosage for oxidative desulfurization were determined to be 95 °C, 6 h, 10 mL, and 0.6 g, respectively. The conversion of refractory sulfur compounds into extractable sulfone forms was verified using gas chromatography. Moreover, the kinetic study confirmed that the designed reaction system follows the pseudo-first-order kinetic model.

Photo-Induced Holes Initiating Peroxymonosulfate Oxidation for Carbamazepine Degradation via Singlet Oxygen

Peroxymonosulfate (PMS) has been intensively used to enhance the photocatalytic activity of catalysts, which is adopted as an electron acceptor to inhibit the recombination of electrons and holes. However, the effect of holes generated by visible light (VL) on PMS activation is always overlooked. Herein, the VL/Bi2WO6/PMS process was constructed for the efficient removal of organics, in which the degradation rate of carbamazepine (CBZ) increased by over 33.0 times by the introduction of PMS into Bi2WO6 under visible light. The radical quenching and determination experiments confirmed that the photogenerated holes could firstly oxidize PMS to form SO5•− and react with HSO5− to produce 1O2, then inducing the formation of other reactive species to greatly enhance the performance of pollutant removal by the VL/Bi2WO6/PMS process. Density functional theory (DFT) predicted that sites with high Fukui index (f0) on CBZ were more susceptible to being attacked, resulting in hydroxylation, ring closure, and C=C bond cleavage of CBZ. Toxicity estimation indicated that photocatalysis degradation products from CBZ were less toxic compared to the parent compound. This study provides a potential avenue for improving photocatalytic efficiency and widening the application of photocatalytic technology in wastewater purification.

Surface Acidification of BiOI/TiO2 Composite Enhanced Efficient Photocatalytic Degradation of Benzene

A novel BiOI/TiO2 nano-heterojunction was prepared using hydrothermal and sol-gel methods. The composite material was characterized by X-ray diffraction, ultraviolet-visible diffuse reflection spectroscopy, scanning electron microscopy, and transmission electron microscopy. The crystallinity and response to light of BiOI/TiO2 were controlled by preparation conditions such as the optimal solvent condition and heat treatment temperature. The photocatalytic activity of the BiOI/TiO2 catalyst was examined using benzene as a test molecule. The benzene degradation rate of the composite catalyst under visible light was enhanced compared to pure TiO2, thus reaching 40% of the original benzene concentration, which increased further to >60% after surface acidification. The fluorescence spectra, light current, and electron paramagnetic resonance confirmed that the enhanced activity was attributed to carrier separation by the heterojunction. The acid sites and active chlorine of hydrochloric acidification offer a novel mechanism for photocatalytic reactions.

The Suitability of Photocatalyst Precursor Materials in Geopolymer Coating Applications: A Review

Today, the building and construction sector demands environmentally friendly and sustainable protective coatings using inorganic coating materials for safe, non-hazardous, and great performance. Many researchers have been working on sustainable solutions to protect concrete and metal infrastructures against corrosion and surface deterioration with the intention of introducing green alternatives to conventional coatings. This article presents a review of developments of geopolymer pastes doped with different types of photocatalyst precursors including factors affecting geopolymer properties for enhancing coating with photocatalytic performance. Photodegradation using geopolymer photocatalyst has great potential for resolving harmless substances and removing pollutants when energized with ultraviolet (UV) light. Although geopolymer is a potentially new material with great properties, there has been less research focusing on the development of this coating. This study demonstrated that geopolymer binders are ideal precursor support materials for the synthesis of photocatalytic materials, with a significant potential for optimizing their distinctive properties.

Towards the Sustainable Production of Ultra-Low-Sulfur Fuels through Photocatalytic Oxidation

Nowadays, the sulfur-containing compounds are removed from motor fuels through the traditional hydrodesulfurization technology, which takes place under harsh reaction conditions (temperature of 350–450 °C and pressure of 30–60 atm) in the presence of catalysts based on alumina with impregnated cobalt and molybdenum. According to the principles of green chemistry, energy requirements should be recognized for their environmental and economic impacts and should be minimized, i.e., the chemical processes should be carried out at ambient temperature and atmospheric pressure. This approach could be implemented using photocatalysts that are sensitive to visible light. The creation of highly active photocatalytic systems for the deep purification of fuels from sulfur compounds becomes an important task of modern catalysis science. The present critical review reports recent progress over the last 5 years in heterogeneous photocatalytic desulfurization under visible light irradiation. Specific attention is paid to the methods for boosting the photocatalytic activity of materials, with a focus on the creation of heterojunctions as the most promising approach. This review also discusses the influence of operating parameters (nature of oxidant, molar ratio of oxidant/sulfur-containing compounds, photocatalyst loading, etc.) on the reaction efficiency. Some perspectives and future research directions on photocatalytic desulfurization are also provided.

Nanoarchitectonics of Copper Tungsten-Mesoporous Silica with a New Template for Photo Oxidative-Desulfurization of Dibenzothiophene

A novel CuWO4/SiO2 heterojunction catalyst was successfully synthesized using a new sulfonamide derivative. The physical characteristics of the prepared samples were investigated by TGA, XRD, FTIR, SEM, UV, PL, and XPS. The prepared catalysts were applied as a nano photocatalyst for photooxidative desulfurization of dibenzothiophene under visible light using hydrogen peroxide as an oxidant. The photocatalytic oxidative desulfurization performances of the prepared samples were investigated. Various factors as the reaction time, dibenzothiophene concentration, catalyst dose, and the oxidizing agent dose were also studied. The prepared photocatalyst has high desulfurization activity in the removal of DBT under mild conditions. Results showed that the CuWO4/SiO2 exhibited considerably higher activity than neat support SiO2. Such improved photocatalytic activity is mainly attributed to the efficient separation of photogenerated electron–hole pairs on CuWO4/SiO2 heterojunction. Moreover, the synergistic effects of this photocatalytic oxidation and the green oxidant hydrogen peroxide played an essential role in desulfurization. The reaction is pseudo-first-order and can reach 98.6% removal of dibenzothiophene after 70 min and 97.2% after four cycles.

Graphical Abstract

Ionic Liquid-Based Polyoxometalate Incorporated at ZIF-8: A Sustainable Catalyst to Combine Desulfurization and Denitrogenation Processes

An effective and sustainable process capable of simultaneously execute desulfurization and denitrogenation of fuels is in fact an actual necessity in the refinery industry. The key to achieve this goal is the parallel oxidation of sulfur and nitrogen compounds present in fuels, which is only achieved by an active and recovered catalyst. A novel heterogeneous catalyst was successfully prepared by the encapsulation of an imidazolium-based polyoxometalate (POM) into a ZIF-8 framework ([BMIM]PMo₁₂@ZIF-8). This composite material revealed exceptional catalytic efficiency to concurrently proceed with the oxidative desulfurization and denitrogenation of a multicomponent model fuel containing various sulfur and nitrogen compounds. A complete removal of all these compounds was achieved after only one hour and the catalyst system was able to be reused for ten consecutive cycles without loss of efficiency. In fact, an ionic liquid POM was incorporated in the ZIF-8 for the first time, and this composite compound was originally applied as a catalyst for simultaneous oxidative desulfurization and denitrogenation processes.

A Short Review of Aerobic Oxidative Desulfurization of Liquid Fuels over Porous Materials

Oxidative desulfurization (ODS) has attracted much attention owing to the mild working conditions and effective removal of the aromatic sulfur-containing compounds which are difficult to desulfurize using the industrial hydrodesulfurization (HDS) technique. Molecular oxygen in ambient air have been recognized as an ideal oxidant in ODS due to its easy availability, non-toxicity and low cost in recent years. However, molecular oxygen activation under mild operating conditions is still a challenge. Porous materials and their composites have drawn increasing attention due to their advantages, such as high surface area and confined pore space, along with their stability. These merits contribute to the fast diffusion of oxygen molecules and the formation of more exposed active sites, which make them ideal catalysts for aerobic oxidation reactions. The confined space pore size offers a means of catalytic activity and durability improvement. This gives rise to copious attention toward the porous catalysts in AODS. In this review, the progress in the characteristics and AODS catalytic activities of porous catalysts is summarized. Then, emphasis on the molecular oxygen activation mechanism is traced. Finally, the breakthroughs and challenges of various categories of porous catalysts are concluded.

Systematic Assessment of Visible-Light-Driven Microspherical V2O5 Photocatalyst for the Removal of Hazardous Organosulfur Compounds from Diesel

The organosulfur compounds present in liquid fuels are hazardous for health, asset, and the environment. The photocatalytic desulfurization technique works at ordinary conditions and removes the requirement of hydrogen, as it is an expensive gas, highly explosive, with a broader flammability range and is declared the most hazardous gas within a petroleum refinery, with respect to flammability. The projected work is based on the synthesis of V2O5 microspheres for photocatalytic oxidation for the straight-run diesel (SRD) and diesel oil blend (DOB). The physicochemical properties of V2O5 microspheres were examined by FT-IR, Raman, UV-vis DRS, SEM, and Photoluminescence evaluations. The as-synthesized photocatalyst presented a trivial unit size, a narrow bandgap, appropriate light-capturing capability, and sufficient active sites. The desulfurization study discovered that the anticipated technique is substantial in desulfurizing DOB up to 37% in 180 min using methanol as an interfacing agent. Furthermore, the outcome of employing a range of polar interfacing solvents was examined, and the 2-ethoxyethanol elevated the desulfurization degree up to 51.3%. However, the anticipated technology is constrained for its application in sulfur removal from SRD. Additionally, the mechanism for a photocatalytic reaction was seen in strong agreement with pseudo-first-order kinetics. The investigated photocatalyst exhibited a compromised recyclability and regeneration tendency.

KIT-6 induced mesostructured TiO2 for photocatalytic degradation of methyl blue

In this study, titania/silica nanocomposite and mesoporous TiO₂ (m-TiO₂) photocatalysts are developed by KIT-6 template via a sol-gel approach. The synthesized photocatalysts are characterized by XRD, EDX, SEM, Raman, PL, and UV-vis DRS analysis techniques. The as-synthesized series revealed a high surface area, smaller size, a greater number of accessible active sites, and enhanced light-harvesting capability. The m-TiO₂ photocatalysts' charge recombination capability was curiously inferior to the rest of as-synthesized TiO₂/KIT-6 nanocomposite materials. The band-gap of as-synthesized materials were suitable for their activity in UV light irradiations. It was pragmatic that the photocatalytic degradation efficiency of m-TiO₂ photocatalysts was superior as compared to that of commercial TiO₂ photocatalyst under UV light irradiations, owing to the synergistic outcome of the anatase phase and a greater number of accessible active-sites availability as a result of high surface area. Moreover, the m-TiO₂ was critically evaluated by investigating various parameters affecting the photocatalytic degradation reaction of MB including the effect of irradiation time, pH, catalyst dosage, and dye concentration. The m-TiO₂, 45wt% composite material and commercial-TiO₂ exhibited 99.27, 91.20, and 84.67% degradation of methyl blue in 50 min, respectively. Finally, the m-TiO₂ exhibited excellent recyclability with negligible loss of activity performance.