Solar-driven Photocatalysis Research Articles

Synergistic photocatalytic degradation of methylene blue using TiO2 composites with activated carbon and reduced graphene oxide: a kinetic and mechanistic study

This comprehensive study explored the removal of methylene blue (MB) from aqueous solutions as a model pollutant, utilizing solar-driven photocatalysis with nano-sized titanium dioxide (TiO2) and composites with activated carbon (AC) and reduced graphene oxide (RGO). This research introduces continuous solar reactor instead of conventional batch experiments investigating its design configuration. Utilizing response surface methodology (RSM), the study determined the optimal process conditions (MB concentration at 30 mg/L, pH 8.82, irradiation time 138 min), under which TiO2 achieved a 93.13% MB removal efficiency. The study further revealed that the integration of TiO2 with AC and RGO (5% wt.) significantly enhanced the MB photocatalytic degradation. The TiO2/AC composite achieved 98.3% MB degradation in 138 min of solar exposure, related to its large specific surface area of 146 m2/g and a pore volume of 0.439 cm3/g. Likewise, the TiO2/RGO composite demonstrated 97% removal with a surface area of 102 m2/g and a pore volume of 0.476 cm3/g, significantly better than nano-TiO2. Additionally, the research investigated the role of the solar reactor configuration on MB removal. Using 26 mm Pyrex tube diameter with 15 cm long on parabolic aluminum concentrator inclined at 30° optimally achieved the peak MB degradation efficiency. Recyclability tests shown a noticeable decrease in nano-TiO2 efficiency to 56.03% without regeneration; however, after regeneration following the third cycle, the efficiency significantly recovered to 70.07%. Thereby, this paper introduces an innovative, continuous, and well-designed solar reactor system for dye removal, employing nano-TiO2 and its composites with AC and RGO for improved photocatalytic efficiency under statistically optimized process conditions.

Enhanced Photocatalytic Properties and Photoinduced Crystallization of TiO2-Fe2O3 Inverse Opals Fabricated by Atomic Layer Deposition.

The use of solar energy for photocatalysis holds great potential for sustainable pollution reduction. Titanium dioxide (TiO2) is a benchmark material, effective under ultraviolet light but limited in visible light utilization, restricting its application in solar-driven photocatalysis. Previous studies have shown that semiconductor heterojunctions and nanostructuring can broaden the TiO2's photocatalytic spectral range. Semiconductor heterojunctions are interfaces formed between two different semiconductor materials that can be engineered. Especially, type II heterojunctions facilitate charge separation, and they can be obtained by combining TiO2 with, for example, iron(III) oxide (Fe2O3). Nanostructuring in the form of 3D inverse opals (IOs) demonstrated increased TiO2 light absorption efficiency of the material, by tailoring light-matter interactions through their photonic crystal structure and specifically their photonic stopband, which can give rise to a slow photon effect. Such effect is hypothesized to enhance the generation of free charges. This work focuses on the above-described effects simultaneously, through the synthesis of TiO2-Fe2O3 IOs via multilayer atomic layer deposition (ALD) and the characterization of their photocatalytic activities. Our results reveal that the complete functionalization of TiO2 IOs with Fe2O3 increases the photocatalytic activity through the slow photon effect and semiconductor heterojunction formation. We systematically explore the influence of Fe2O3 thickness on photocatalytic performance, and a maximum photocatalytic rate constant of 1.38 ± 0.09 h-1 is observed for a 252 nm template TiO2-Fe2O3 bilayer IO consisting of 16 nm TiO2 and 2 nm Fe2O3. Further tailoring the performance by overcoating with additional TiO2 layers enhances photoinduced crystallization and tunes photocatalytic properties. These findings highlight the potential of TiO2-Fe2O3 IOs for efficient water pollutant removal and the importance of precise nanostructuring and heterojunction engineering in advancing photocatalytic technologies.

TiO2-based heterojunctions for photocatalytic hydrogen evolution reaction

Solar-driven photocatalysis hydrogen evolution is a promising method to generate hydrogen from water, a green and clean energy source, using solar and semiconductors. Up to now, TiO2 still represents the most inexpensive and widely studied metal oxide semiconductors for photocatalysis. TiO2 coupling with other semiconductors to form heterojunctions is considered an efficient way to improve photocatalytic performances. In this review, TiO2-based heterojunctions are classified into conventional, p-n type, Z-scheme, S-scheme, and other heterojunctions based on their band structures. The photocatalytic mechanisms of various types of heterojunctions are described in detail. In order to rationally design and better synthesize heterojunctions with excellent performance, the contribution of theoretical calculations to the field of TiO2-based heterojunction photocatalysts and the key role of theoretical prediction are also discussed. Finally, the opportunities and current challenges to promote photocatalytic performance are provided to assist the design of TiO2-based heterojunction photocatalysts with superior performance.

Carbon-dots-conjugated semiconductors for enhanced solar-driven photocatalysis

Carbon-dots-conjugated semiconductors for enhanced solar-driven photocatalysis

Cu-doped TiO2 spheres: enhanced solar-driven photocatalysis for hydrogen generation and degradation of methylene blue and Congo red

Cu-doped TiO2 spheres: enhanced solar-driven photocatalysis for hydrogen generation and degradation of methylene blue and Congo red

Interface engineered cascade-type electronic structure of 2D/0D/2D CdS–CdCO3/SnO2 quantum dots/g-C3N4 nanocomposite for boosting solar-driven photocatalysis

A rational design of heterojunctions with high-quality contacts is essential for efficiently separating photogenerated charge carries and boosting the solar-driven harvesting capability. Herein, we fabricated a novel heterojunction of SnO2 quantum dots–anchored CdS–CdCO3 with g-C3N4 nanosheets as a superior photocatalyst. SnO2 quantum dots (SQDs) with positively charged surfaces were tightly anchored on the negatively charged surface of CdS nanosheets (NSs). The resulting CdS@SnO2 was finally decorated with g-C3N4 NSs, and a new crystalline phase of CdS–CdCO3 was formed during the hydrothermal decoration process, g-C3N4 decorated CdS–CdCO3@SnO2 (CdS–CdCO3@SnO2@g-C3N4). The as-synthesized photocatalysts were evaluated for the degradation of methyl orange dye under solar light conditions. The CdS–CdCO3@SnO2@g-C3N4 exhibited 7.7-fold and 2.3-fold enhancements in photocatalytic activities in comparison to those of the bare CdS and CdS@SnO2 NSs, respectively. The optimal performance of CdS–CdCO3@SnO2@g-C3N4 is primarily attributed to the cascade-type conduction band alignments between 2D/0D/2D heterojunctions, which can harvest maximum solar light and effectively separate photoexcited charge carriers. This work provides a new inspiration for the rational design of 2D/0D/2D heterojunction photocatalyst for green energy generation and environmental remediation applications.

Metal Poly(heptazine imides) as Multifunctional Photocatalysts for Solar Fuel Production.

Solar-driven photocatalysis employing particulate semiconductors represents a promising approach for sustainable production of valuable chemical feedstock. Metal poly(heptazine imide) (MPHI), a novel 2D ionic carbon nitride, has been recognized as an emerging photocatalyst with distinctive properties. In this minireview, we first delineate the forefront innovations of MPHI photocatalysts, spanning from synthetic strategies and solving structures to the exploration of novel properties. We place special emphasis on the structural design principles aimed at developing high-performance MPHI systems toward photocatalytic solar fuel production such as H2 evolution, H2O oxidation, H2O2 production and CO2 reduction. Finally, we discuss crucial insights and challenges in leveraging highly active MPHIs for efficient solar-to-chemical energy conversion.

Immobilization of Bi2MoO6/ZnO heterojunctions on glass substrate: Design of drug and dye mixture degradation by solar-driven photocatalysis

In this study, the Bi2MoO6/ZnO heterostructures were quickly and easily obtained using the sonochemical method and impregnated on a glass plate using epoxy resin. The influence of increasing the percentage of ZnO (1:1, 2:1, 4:1 and 8:1% by weight) in relation to Bi2MoO6 on the formation of the heterostructure was investigated. The XRD results of the heterostructures indicated the presence of ZnO phases with a hexagonal structure and Bi2MoO6 with an orthorhombic structure. According to FESEM and HRTEM analyses, the morphology of ZnO is controlled with the addition of Bi2MoO6. The photocatalytic activity of the heterostructures was evaluated using a mixture (MIX) of methylene blue dye and diclofenac potassium, obtaining photocatalytic efficiency of 99.7 % and 90 % in 100 min under solar irradiation, with the ZN8B1 heterostructure, respectively. Aiming to increase the reuse of the material, the ZN8B1 heterostructure was impregnated into a glass plate, obtaining an efficiency of on average 65.2 % for 10 reuse cycles, showing that the impregnate can be applied to effluent treatment. The evaluation of the effect of photocatalyst dosage, contaminant concentration and pH effect was carried out with the MIX solution in order to simulate real conditions. Furthermore, a possible photocatalytic mechanism was proposed based on inhibition tests, verifying that the •O2– and •OH radicals were the dominant active species, which followed the Z-scheme mechanism.

Controlled solvothermal synthesis of self-assembled SrTiO3 microstructures for expeditious solar-driven photocatalysis dye effluents degradation

In this work, the self-assembled SrTiO3 (STO) microstructures were synthesized via a facile one-step solvothermal method. As the solvothermal temperature increased from 140 °C to 200 °C, the STO changed from a flower-like architecture to finally an irregularly aggregated flake-like morphology. The photocatalytic performance of as-synthesized samples was assessed through the degradation of rhodamine B (RhB) and malachite green (MG) under simulated solar irradiation. The results indicated that the photocatalytic performance of STO samples depended on their morphology, in which the hierarchical flower-like STO synthesized at 160 °C demonstrated the highest photoactivities. The photocatalytic enhancement of STO-160 was benefited from its large surface area and mesoporous configuration, hence facilitating the presence of more reactive species and accelerating the charge separation. Moreover, the real-world practicality of STO-160 photocatalysis was examined via the real printed ink wastewater-containing RhB and MG treatment. The phytotoxicity analyses demonstrated that the photocatalytically treated wastewater increased the germination of mung bean seeds, and the good reusability of synthesized STO-160 in photodegradation reaction also promoted its application in practical scenarios. This work highlights the promising potential of tailored STO microstructures for effective environmental remediation applications.

Fenton-mediated solar-driven photocatalysis of industrial dye effluent with polyaniline impregnated with activated TiO2-Nps

Various integrated technologies have been investigated for the remediation of heavily polluted industrial dye effluent. Also, more than 70 % of these dyes are known to be solely azo dyes used in the textile industry with 5–30 % presence in the effluent as loose dye molecules which are recalcitrant to treatment. These challenges led to the investigation of energy-efficient processes (solar) and the fabrication of high-performance nano-photocatalysts for proficient photocatalysis of dye effluent while mediating the process with Fenton reagents. The study fabricated nanopolymeric catalyst composites (P-AKT) via novel in situ coupling and impregnation of the polyaniline (PANI) with surface-activated TiO2 NPs. This fabrication is aimed at developing a high-performance catalyst with rapid and proficient photocatalytic activities to photons from sunlight irradiation. The photocatalytic process was mediated using a novel Fenton reagent to enhance the generation of radical species for dye degradation. Various instrumental characterization methods were used to study the structural, molecular, elemental, functional and optoelectronic properties of the fabricated nanocomposite photocatalysts. The result reveals functional groups aiding dye-catalyst bonding and morphological interaction reveal a surface-activated tetragonal crystalline mixture of anatase and rutile from TiO2−Nps embedded in the macromolecular chain of PANI. It also reveals the optimal conditions of 20 mg dosage, 10 mg/L initial concentration with substantial effectiveness at pH of 5 and 7. However, the most efficient photocatalyst recorded was P-AKT-2 % and P-AKT-3 % having 95 % and 94 % efficiencies at 90 min of solar irradiation. The photocatalyst equally demonstrated its capacity for effluent treatability up to 4 cycles of use.

Room-temperature photooxidation of low-concentration coalbed methane to methanol over CuOx/D-WO3 combined with gas-solid-liquid interface: From pollutant to clean fuel

Direct transformation of CH4 in low-concentration coalbed methane (LC-CBM) to clean fuel methanol is a more sustainable route as industrial CH4 transformation is usually energy-intensive. Solar-driven photocatalysis with near-zero carbon emissions can activate and transform CH4 at ambient temperatures, whereas the reported methanol productivities of traditional solid-liquid photocatalysis are still far from satisfactory. Herein, amorphous CuOx decorated defective WO3 nanocomposites (CuOx/D-WO3) were first synthesized and used as full-spectrum responsive photocatalysts for selective oxidation of LC-CBM to methanol. Introducing oxygen vacancies endows CuOx/D-WO3 with near-infrared (NIR) response. Loading CuOx boosts the separation of photogenerated charge carriers and the generation of ·OH via H2O2 reduction by photoelectrons on CuOx sites, confirmed by photoelectrochemical characterizations and in-situ XPS. Under simulated solar light irradiation, CuOx/D-WO3 exhibited significantly promoted activity of CH4 oxidation compared with the counterpart D-WO3. Even under NIR illumination, the optimal 3.0 % CuOx/D-WO3 showed a methanol production of 1.57 mmol·gcat−1 with selectivity of 79.8 %. Furthermore, a gas-solid-liquid triphase interface was constructed by immobilizing hydrophilic 3.0 % CuOx/D-WO3 on superhydrophobic carbon fiber paper (CFP) to promote methanol generation through strengthening CH4 mass transfer. This triphase photocatalysis exhibited a methanol production of 25.42 mmol·gcat−1, which was ∼4 times higher than solid-liquid diphase catalysis. Methanol selectivity of CuOx/D-WO3/CFP triphase photocatalysis was up to 95.3 %. It was mainly due to enhanced mass transfer of CH4 from gas phase to photocatalysts layer through hydrophobic-hydrophilic wettability abrupt interface of CuOx/D-WO3/CFP, which could be evidenced by significantly increased ·CH3 radicals from in-situ EPR spectra. This work broadens the avenue toward cleaner and efficient utilization of LC-CBM in a sustainable way.

Morphological regulation of CdS/Ga0.04Cd0.96S nanocomposites for enhanced efficiency of solar-driven rhodamine B degradation

In recent years, semiconductor-based nanocomposites have emerged as promising materials for solar-driven photocatalytic degradation of organic pollutants. In this study, GaxCd1−xS nanospheres were successfully synthesized through the interstitial doping of Ga ions into CdS nanospheres via a hydrothermal route. These nanospheres were further employed to create CdS NRs/Ga0.04Cd0.96S nanocomposites using solvothermal methods, aiming to enhance the efficiency of solar-driven rhodamine B (Rh-B) degradation. The photocatalytic activities of the prepared CdS nanostructures, Ga0.04Cd0.96S nanospheres, and CdSNRs/Ga0.04Cd0.96S nanocomposites were evaluated for dye removal and photocatalytic degradation. Notably, Ga0.04Cd0.96S (1:30) nanospheres exhibited high efficiency in degrading Rh-B compared to pure CdS nanostructures under identical reaction conditions. Single CdS NRs/Ga0.04Cd0.96S (1:1) demonstrated stable cyclic photocatalytic performance over multiple rounds of use. The study further elucidated the enhanced separation and lower recombination of photogenerated electrons and holes in CdS NRs/Ga0.04Cd0.96S compared to Ga0.04Cd0.96S, as confirmed by PL spectrum and photocurrent response studies. The scavenger method was employed to identify reactive species, providing insights into the mechanism of Rh-B degradation. Additionally, the proposed mechanism of photocatalytic degradation of Rh-B over the CdS NRs/Ga0.04Cd0.96S nanocomposites was discussed. This research contributes valuable insights into the development of efficient semiconductor-based nanocomposites for solar-driven photocatalysis, addressing environmental concerns related to organic pollutant degradation.

Boosted solar-driven photocatalysis: silver molybdate/reduced graphene oxide nanocomposites for methylene blue decomposition

Boosted solar-driven photocatalysis: silver molybdate/reduced graphene oxide nanocomposites for methylene blue decomposition

Solar-driven photocatalytic reduction of copper(ii) to copper(i) and zerovalent copper (Cu(0)): a sustainable approach for solar recovery of copper on a pilot scale

This study demonstrates a sustainable pilot-scale recovery of metallic copper from Cu(ii) using solar-driven photocatalysis with ZnO and POPD/ZnO photocatalysts. Achieving an 80% recovery rate, this process produces zerovalent copper and marks the 100% solar-recovered copper coin.

Glucose photorefinery for sustainable hydrogen and value-added chemicals coproduction

As a naturally occurring and stable energy supply, biomass will be the leading renewable energy in the future, and its high-value application will help promote the realization of carbon neutrality. Glucose, as the basic unit of lignocellulosic biomass, has been widely investigated as the feedstock to produce various value-added chemicals. Compared to the traditional glucose valorization platforms, such as thermal catalysis and biological fermentation, solar-driven photocatalysis holds the advantages in mild reaction conditions and controllable reaction kinetics, and it is emerging as a sustainable and efficient technology for glucose conversion. With the rational design of the photocatalysts, glucose could be selectively converted into specified chemicals via oriented bond cleavage along with the sustainable generation of hydrogen at the same time, which is the so-called glucose photorefinery process. This present review introduces the general principles and latest progress in glucose photorefinery. The rational design of bifunctional photocatalysts to achieve extended light absorption, efficient charge separation, and favorable surface reaction is also introduced. The oriented breakage of the chemical bonds in glucose molecules to produce different chemicals on different active sites is highlighted. Finally, challenges and perspectives on glucose photorefinery to achieve further efficiency and more fruitful reaction pathways are proposed. This present review is believed to provide guidance for the biomass valorization by mild photocatalysis to simultaneously produce sustainable fuels and chemicals with the rational design of dually functional photocatalysts.

Solar-driven photodegradation of ciprofloxacin and E. coli growth inhibition using a Tm3+ upconverting nanoparticle-based polymer composite

Solar-driven photocatalysis is of great interest in terms of a sustainable use of energy and its application in wastewater treatment. The UV light-driven photogeneration of H2O2 by solar irradiation is an advanced strategy for the treatment of bacteria and recalcitrant pollutants in wastewater, but suffers from low efficiencies. In this work, a solar-driven multifunctional nanocomposite consisting of Tm3+ upconverting nanoparticles, poly(vinyl alcohol), poly(acrylic acid) and hydroxylated sulfonated poly(ether ether ketone) was prepared. The components were crosslinked via a heating treatment at 170 °C, resulting in a non-leaching porous material. This nanocomposite exhibited excellent adsorption ability (89 % in 150 min) toward a 100 mg/L ciprofloxacin aqueous solution and proved to photodegrade it (50 %) upon 4 h artificial solar irradiation, exploiting photon upconversion processes. Moreover, an 80 % bactericidal effect against E. coli was registered upon sunlight irradiation. Altogether, these results suggest the feasibility of a solar-driven wastewater treatment based on upconverting nanoparticles.

Tailoring morphology and structure of 1D/2D isotype g-C3N4 for sonophotocatalytic hydrogen evaluation

Solar-driven photocatalysis is a promising technology for producing clean energy and pollutant removal. The efficiency of the photocatalytic applications is limited by inefficient light harvesting and faster electron–hole recombination of semiconductors. An external force such as ultrasound irradiation could overcome the limitation of the light absorption of the photocatalyst and enhance the production of energy sources. In this work, we have built an effective interphase boundary between two different morphologies of carbon graphitic nitride (g-C3N4). The isotype heterostructure is confirmed through the structure changes using XRD, the 1D/2D morphology formation using SEM and TEM imaging, and the bands’ position through Mott–Schottky and VB-XPS measurements. The designed 1D/2D g-C3N4 isotype heterostructure showed significant improvements through photocatalytic and sonophotocatalytic hydrogen evolution reactions (HER). Sonophotocatalytic HER of R-g, S-g, and RS-g samples showed enhanced by 3.9, 5.3, and 6.77 folds compared to the photocatalysis system. This research affords the possibility of developing intrinsic photocatalysts with different phases or morphology for efficient photocatalytic or sonophotocatalytic applications.

Solar-driven photocatalysis for recycling and upcycling plastics

The widespread use of plastics in modern societies generates huge amounts of plastic waste. With a view toward sustainability, researchers are now seeking strategies for recycling and upcycling plastic waste to valuable products. There is currently a significant amount of research on thermal catalytic recycling of plastics. These studies are mostly limited by high energy input, and the economic efficiency of the reaction process is not ideal. Photocatalysis and photothermal catalysis show superiority in terms of energy compared to traditional thermal catalysis. Recent researches about photocatalysis and photothermal catalysis to achieve chemical recycling and upcycling of plastics are reviewed, especially for the concept and application of three types of photothermal catalytic processes. Considering the most important efficiency, energy, and separation issues in plastic recycling, photothermal catalysis has a huge potential in the future field of plastic chemical recycling and upcycling.

Ultrafast Hole Transfer in Graphitic Carbon Nitride Imide Enabling Efficient H2O2 Photoproduction.

Solar-driven photocatalysis is a promising approach for renewable energy application. H2O2 photocatalysis by metal-free graphitic carbon nitride has been gaining attention. Compared with traditional thermal catalysis, metal-free graphitic carbon nitride photocatalysis could lower material cost and achieve greener production of H2O2. Also, to better guide photocatalyst design, a fundamental understanding of the reaction mechanism is needed. Here, we develop a series of model cost-effective metal-free H2O2 photocatalysts made from graphitic carbon nitride (melem) and common imide groups. With 4,4'-oxydiphthalic anhydride (ODPA)-modified g-C3N4, a H2O2 yield rate of 10781 μmol/h·g·L could be achieved. Transient absorption and ex situ Fourier transform infrared (FTIR) measurements revealed an ultrafast charge transfer from the melem core to water with ∼3 ps to form unique N-OH intermediates. The electron withdrawing ability of the anhydride group plays a role in governing the rate of electron transfer, ensuring efficient charge separation. Our strategy represents a new way to achieve a low material cost, simple synthesizing strategy, good environment impact, and high H2O2 production for renewable energy application.

Layered MoS2: effective and environment-friendly nanomaterial for photocatalytic degradation of methylene blue

Photocatalytic degradation is a promising method for removing persistent organic pollutants from water because of its low cost (see solar-driven photocatalysis), high mineralisation of pollutants, and low environmental impact. Photocatalysts based on transition metal dichalcogenides (TMDs) have recently attracting high scientific interest due to their unique electrical, mechanical, and optical properties. A MoS2 photocatalyst of the layered structure was managed to photodegrade methylene blue (MB) under visible light irradiation. The catalyst was thoroughly characterised using SEM, AFM, powder XRD, UV–Vis, Raman, and XPS measurements. The photocatalytic degradation of the MB solution was conducted under the following conditions: (i) reductive and (ii) oxidative. The impact of optical and electronic properties, and the MoS2-MB interaction on photocatalytic activity, was discussed. The apparent rate constants (kapp) of degradation were 3.7 × 10–3; 7.7 × 10–3; 81.7 × 10–3 min−1 for photolysis, oxidative photocatalysis, and reductive photocatalysis. Comparison of the degradation efficiency of MB in reductive and oxidative processes indicates the important role of the reaction with the surface electron. In the oxidation process, oxygen reacts with an electron to form a superoxide anion radical involved in further transformations of the dye, whereas, in the reduction process, the addition of an electron destabilises the chromophore ring and leads to its rupture.