Efficient Visible-light Photocatalyst Research Articles

Synthesis and Photocatalytic Application of Magnetic CoFe2O4/Conjugated Poly(vinyl chloride) Derivative Nanocomposite.

CoFe2O4 has potential for application as a magnetically recoverable visible-light photocatalyst, but its photocatalytic activity is encumbered by the high recombination probability of its photogenerated holes (h+) and electrons (e-). This work was undertaken to boost the photocatalysis of CoFe2O4 through coupling with conjugated poly(vinyl chloride) derivative (CPVC). An easily implementable solvothermal-liquid solid mixing-evaporation of the solvent-pyrolysis method was exploited to synthesize CoFe2O4/CPVC nanocomposites. The photocatalytic capabilities of the products were assessed through photocatalyzing the reduction of Cr(VI) under visible-light (λ > 420 nm). The results demonstrate that the optimal CoFe2O4/CPVC nanocomposite (CoFe2O4/CPVC-2) has markedly heightened photocatalytic activity (3.6 times that of CoFe2O4) and competent reusability and is magnetically recoverable. Furthermore, CoFe2O4/CPVC-2 also shows superior performance toward photocatalytic treatment of the diluted Cr(VI)-containing passivation solution of copper alloys. It is deduced based on the photoelectricity measurement results that the increased photocatalysis of CoFe2O4/CPVC-2 is chiefly attributed to its p-n heterojunction structure, which greatly elevates the h+-e- separation and transfer efficiency. When waste PVC plastic films (replacing the new pure PVC powder) were utilized for the synthesis, the obtained CoFe2O4/CPVC nanocomposite exhibited even better photocatalytic activity (4 times that of CoFe2O4). This work not only has made a new magnetically recoverable, efficient visible-light photocatalyst for decontamination of Cr(VI) in water but also is inspirational for recycling PVC plastic waste to produce high-valued visible-light photocatalysts.

Solvothermal synthesis of CdTiO3/Ti3C2 MXene composite as a new efficient visible light photocatalyst

Solvothermal synthesis of CdTiO3/Ti3C2 MXene composite as a new efficient visible light photocatalyst

Copper Doping Induced Band Structure and Morphology Transformation in CaTiO3 for Textile Dye Photodegradation Applications

Semiconductor metal oxide with a wide bandgap like CaTiO3 can be exploited into an efficient visible light photocatalyst via cation doping. The type of dopant and the site of doping is known to greatly influence the photocatalytic activity of a material. Based on the intricacies of the density functional theory electronic structure study and we delve into the optimization of one-pot solvothermal synthesis to obtain Cu doped CaTiO3 nanocuboids. Doping of copper not only resulted in change in the electronic structure of the material but also led to change in the morphology. The uneven nanostep architecture resulted in increase in the surface area of the catalyst which led to more active sites for the adsorption of the dyes and subsequent degradation. The reduced band gap and decreased recombination of charge carriers made the copper doped calcium titanate an efficient photocatalyst for degradation of both cationic (99.7% degradation of MV dye in 120minutes) and anionic (99.8% degradation of RB in 45minutes) dyes.

Nitrogen-Rich Triazine-Based Covalent Organic Frameworks as Efficient Visible Light Photocatalysts for Hydrogen Peroxide Production.

Covalent organic frameworks (COFs) have been widely used in photocatalytic hydrogen peroxide (H2O2) production due to their favorable band structure and excellent light absorption. Due to the rapid recombination rate of charge carriers, however, their applications are mainly restricted. This study presents the design and development of two highly conjugated triazine-based COFs (TBP-COF and TTP-COF) and evaluates their photocatalytic H2O2 production performance. The nitrogen-rich structures and high degrees of conjugation of TBP-COF and TTP-COF facilitate improved light absorption, promote O2 adsorption, enhance their redox power, and enable the efficient separation and transfer of photogenerated charge carriers. There is thus an increase in the photocatalytic activity for the production of H2O2. When exposed to 10 W LED visible light irradiation at a wavelength of 420 nm, the pyridine-based TTP-COF produced 4244 μmol h-1 g-1 of H2O2 from pure water in the absence of a sacrificial agent. Compared to TBP-COF (1882 μmol h-1 g-1), which has a similar structure but lacks pyridine sites, TTP-COF demonstrated nearly 2.5 times greater efficiency. Furthermore, it exhibited superior performance compared to most previously published nonmetal COF-based photocatalysts.

BiOBr-rice husk carbon composite for antibiotic degradation

Highly efficient visible light photocatalysts are necessary to address the water pollution caused by antibiotics. In the present study, bismuth oxybromide-rice husk-derived carbon (BiOBr-RHC) composites (with different wt% of RHC) were prepared via a simple solid-state method. Results of the studies indicate that the use of rice husk carbon has a considerable effect on the degradation of the commonly used fluoroquinolone antibiotic norfloxacin (NOR). BiOBr-RHC-10 exhibits the highest catalytic degradation towards NOR under visible light irradiation among the developed composite catalysts. Introducing carbon in the composites provides better separation of charge carriers, thereby reducing the recombination rate of electron-hole pairs. The promising visible-light-driven catalytic activity of the BiOBr-RHC composite makes it a potential candidate for the effective degradation of the antibiotic present in wastewater.

Coupling Z-Scheme g-C3N4/rGO/MoS2 Ternary Heterojunction as an Efficient Visible Light Photocatalyst for Hydrogen Evolution and RhB Degradation.

Coupling heterostructures to synergistically improve the light adsorption and promote the charge carrier separation has been regarded as an operative approach to advance the photocatalytic performances. However, it is still challenging to construct heterostructures with appropriate optical properties and interfacial energy structures at the same time. In this work, a Z-scheme g-C3N4/rGO/MoS2 ternary composite photocatalyst is successfully synthesized via an effective hydrothermal method. The as-synthesized g-C3N4/rGO/MoS2 composite photocatalyst exhibited significant improvement for visible light absorption and boosted the separation efficiency of photoinduced electron-hole pairs. The g-C3N4/rGO/MoS2 system exhibited optimum visible-light-induced photocatalytic activity in hydrogen (H2) from water splitting and degrading pollutant rhodamin B (RhB), which is 22 times and 5 times higher than that of pure g-C3N4, respectively. The excellent photocatalytic activities are attributed to the synergetic effects of coupling rGO, g-C3N4, and MoS2 ternary structures to the composite photocatalyst. These combinations of intimate two-dimensional nanoconjugations can effectively inhibit charge recombination and accelerate charge transfer kinetics, forming a Z-scheme-assisted photocatalytic mechanism, thereby exhibiting superior photocatalytic activity.

High carrier mobility ZrSSe/SnX (X=S, Se, S2, Se2) vdW heterostructures for photocatalytic overall water splitting: A first-principles study

Recently, the assembly of novel two-dimensional materials via van der Waals (vdW) interactions to form heterostructures is considered an effective strategy for producing materials with enhanced photocatalytic activities. This study systematically explored the optoelectronic and photocatalytic properties and carrier mobilities of novel ZrSSe/SnX (X = S, Se, S2, Se2) vdW heterostructures using density functional theory. The formation energies, elastic constants, phonon dispersions, and results of ab-initio molecular dynamic simulations indicate structural, mechanical, dynamic, and thermal stability. The electronic band structure and optical properties are calculated using hybrid functional HSE06 for accurate calculations. The results of calculations using the bandgap center technique based on density functional theory show that ZrSSe/SnSe, ZrSSe/SnS2, and ZrSSe/SnSe2 heterostructures possess suitable band edges for photocatalytic overall water splitting. The optical absorption spectrum covers a broad range from 104 in the visible region and increases to 105 in the UV region. Furthermore, the ZrSSe/SnX (X = S, Se, S2, Se2) heterostructures have high carrier mobilities of the order of 105. High mobilities help carriers to move quickly and reduce the recombination rate of holes and electrons. The findings indicate that ZrSSe/SnX (X = S, Se, S2, Se2) heterostructures are potentially efficient visible-light photocatalysts for overall water splitting.

KCl mediated Ag/Co@Fe2O3/C3N4 heterojunction as a highly efficient visible photocatalyst for tetracycline degradation: Application of machine learning

In this work a new KCl mediated Ag/Co@Fe2O3/C3N4 heterojunction was synthesized by a simple coprecipitation method and was characterized. The band gap of the synthesized heterojunction was calculated as 2.1ev indicating its good potential for using as visible light photocatalyst. The synthesized heterostructure was used for photodegradation of tetracycline and the experimental conditions were optimized. The results showed with 0.04g of heterostructure catalyst, the degradation of tetracycline 50ppm can be perform in a short time (40 min ) with efficiency 100%. The enhanced photoactivity of this catalyst is due to unique structure of KCl mediated Ag/Co@Fe2O3/C3N4 heterojunction that can decrease the charge recombination and therefore, leading highly efficient visible light photocatalyst. Experimental data also were analyzed using various regression models based on machine learning techniques, particularly neural networks. The outcomes reveal the effectiveness of neural network models as they demonstrate negligible Mean Root Squared Error (MRSE) values and nearly perfect R-squared scores. This highlights the excellence and accuracy of the neural network models in capturing and predicting the patterns and trends within the experimental data.

Fabrication of WO3 photocatalyst by plasma assisted ball milling under different discharge atmospheres

A convenient method for producing single oxide WO3-x at room temperature through plasma milling was reported, resulting in a highly efficient visible-light photocatalyst. By altering the discharge atmosphere during plasma milling from ammonia and nitrogen to argon, the color of the milled monoclinic WO3 powders deepens from blue to dark blue, indicating an increased concentration of oxygen vacancies. The morphological and structural properties of the monoclinic WO3 powders, prepared using different ball milling techniques, are characterized using XRD, SEM, TEM, Raman, XPS, EPR, and UV–vis. These results reveal that plasma milling leads to a higher surface area, increased presence of oxygen vacancies, and more defects compared with conventional milling, resulting in a greater number of more reactive sites and a larger contact area between monoclinic WO3 nanoparticles and RhB solution. Consequently, monoclinic WO3 samples fabricated through Ar-P-milling exhibit the highest photocatalytic activity. This is attributed to the reduction of the WO3−x band gap to 2.28 eV by Ar-P-milling with high oxygen vacancies. This lower bandgap markedly improves the light utilization rate, thereby enhancing the overall photocatalytic efficiency. The Ar-P-milled WO3 shows the highest degradation rate constant of 0.037 min−1, which is 4 times higher than that of pure monoclinic WO3.

Highly efficient visible-light photocatalyst Ag/Ag3PO4/Bi2O2CO3 enabled by the synergistic effect of heterojunction and surface plasma resonance

Highly efficient visible-light photocatalyst Ag/Ag3PO4/Bi2O2CO3 enabled by the synergistic effect of heterojunction and surface plasma resonance

Two-Dimensional Cu-Porphyrin Metal-Organic Framework Nanosheet-Supported Flaky TiO2 as an Efficient Visible-Light-Driven Photocatalyst for Dye Degradation and Cr(VI) Reduction.

A series of 2D M(Cu, Zn, Co, and Mn)-TCPP MOFs/TiO2 binary nanocomposites (TCPP = tetrakis(4-carboxyphenyl)porphyrin) were constructed by solvothermal in situ loading of flaky TiO2 on the surface of 2D metal-organic frameworks (MOFs). The influence of different coordination metals on the catalytic activity was studied, and it was found that the 2D Cu-TCPP MOFs/TiO2 nanocomposite exhibited the best photo-Fenton performance. The superior property can be attributed to the high absorption coefficient and ultrathin two-dimensional structure of the 2D Cu-TCPP MOFs nanosheets. Meanwhile, the 2D Cu-TCPP MOFs/TiO2 II heterostructure can effectively promote the separation and transfer of photoformed carriers. Moreover, under visible irradiation, the optimized 2D Cu-TCPP MOFs/TiO2 composite can convert 99.9% of Cr(VI) to Cr(III) within 60 min with methanol as the hole scavenger at pH 3.14. Also, the photocatalytic performance of 2D Cu-TCPP MOFs/TiO2 was maintained after five reaction cycles. Furthermore, the proposed visible-light-driven photocatalysis mechanism of the 2D Cu-MOFs/TiO2 composite was reasonably derived according to experimental results. This study demonstrates the potential of building efficient TiO2-based visible light photocatalysts with 2D metal-porphyrin MOFs.

Construction of novel g-C3N4/β-FeOOH Z-Scheme heterostructure photocatalyst modified with carbon quantum dots for efficient degradation of RhB

The degradation of organic pollutants using semiconductor photocatalysts is a new ecological approach, but the currently available photocatalysts are not very efficient. Herein, in order to obtain efficient visible-light photocatalysts, g-C3N4/β-FeOOH-modified carbon quantum dots (CDs) composite photocatalysts with Z-Scheme charge transfer mechanism were successfully synthesized. The phase composition and morphology of the composite were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrophotometry (FT-IR), and X-ray photoelectron spectroscopy (XPS) techniques. Due to the upconversion effect of the CDs, the optical response range of the composite was effectively widened, and the optical utilization rate was improved. The Z-Scheme heterostructure not only improves the light trapping ability, significantly inhibits charge-carrier complexation, and realizes the spatial separation of redox sites, but also ensures that the photocatalyst maintains a suitable valence-conductivity band position and maintains the strong redox reactivity. In addition, CDs have the unique characteristics of electronic storage and transfer, which effectively enhance the quantum separation efficiency of the composite. The photocatalytic efficiency was measured by degrading rhodamine B (RhB) under visible light. The degradation performance was the best when the weight ratio of CDs was 6%, and the RhB solution degradation rate reached 100 % in 60 min. The unique structure and reliable mechanism provide a way for the development of advanced photocatalyst.

Comparative studies of “3d” transition metals (Co, Mn, Ni) doped ZnO nanoparticles for visible light degradation of methylene blue

The development of efficient visible-light photocatalysts is highly desired for a clean and sustainable environment. Herein, we report the fabrication and functionalization of zinc oxide (ZnO) nanostructures for the degradation of organic pollutants, one of the key components of environmental pollution. Pure and “3d” transition metal ions doped ZnO (Zn1−xMxO, where M = Mn, Ni, Co with varying doping concentration x = 1 % and 7 %) were synthesized by co-precipitation method and their structural, electronic, morphological, and optical properties were investigated in detail. The powder X-ray diffraction (XRD) pattern of pure and Zn1−xMxO nanostructures confirmed the hexagonal wurtzite phase (p63mc) with an average crystallite size of around 22–27 nm. The energy dispersive x-ray (EDX) analysis confirmed the presence of metal dopants in ZnO. The morphology of synthesized nanostructures was found to be spherical. The band gap of ZnO was considerably narrowed from 3.15 to 1.8 eV through doping, indicating extension towards visible light absorption. Photoluminescence (PL) emission spectra of doped ZnO revealed a low recombination rate of electrons (e-) and holes (h+) and various possible defect states within the bandgap. Furthermore, electron spin resonance showed the presence of Mn2+ centers. Optimized metal-doped zinc oxide revealed higher photocatalytic activity, during degradation of methylene blue model dye under visible light.

Highly efficient ultrasound-driven Cu-MOF/ZnWO4 heterostructure: An efficient visible-light photocatalyst with robust stability for complete degradation of tetracycline

Metal-organic frameworks (MOFs) are a significant class of porous, crystalline materials composed of metal ions (clusters) and organic ligands. The potential use of copper MOF (Cu-BTC) for the sonophotocatalytic degradation of Tetracycline (TC) antibiotic was investigated in this study. To enhance its catalytic efficiency, S-scheme heterojunction was created by combining Cu-BTC with Zinc tungstate (ZnWO4), employing an ultrasound-assisted hydrothermal method. The results demonstrated that the Cu-BTC/ZnWO4 heterojunction exhibited complete removal of TC within 60 min under simultaneous irradiation of visible light and ultrasound. Interestingly, the sonophotocatalytic degradation of TC using the Cu-BTC/ZnWO4 heterojunction showed superior efficiency (with a synergy index of ∼0.70) compared to individual sonocatalytic and photocatalytic degradation processes using the same heterojunction. This enhancement in sonophotocatalytic activity can be attributed to the formation of an S-scheme heterojunction between Cu-BTC and ZnWO4. Within this heterojunction, electrons migrated from Cu-BTC to ZnWO4, facilitated by the interface between the two materials. Under visible light irradiation, the built-in electric field, band edge bending, and coulomb interaction synergistically inhibited the recombination of electron-hole pairs. Consequently, the accumulated electrons in Cu-BTC and holes in ZnWO4 actively participated in the redox reactions, generating free radicals that effectively attacked the TC molecules. This study offers valuable perspectives on the application of a newly developed S-scheme heterojunction photocatalyst, demonstrating its effectiveness in efficiently eliminating diverse recalcitrant pollutants via sonophotocatalytic degradation.

Data-Driven Discovery of a Covalent Organic Framework Heterojunction as Efficient Photocatalysts for Overall Solar Water Splitting.

Searching for highly efficient visible-light photocatalysts is a high-cost and time-consuming process in the water splitting field. The integration of data-driven screening based on the database and density functional theory calculations represents a promising approach. In this study, we first present a topologically assembled single-layer covalent organic framework (COF) that is used to build a COF heterojunction database via AA stacking. Then we propose a systematic search procedure for COF heterojunctions as overall solar water splitting photocatalysts, including suitable band gap (screen 1), appropriate band edge position (screen 2), spontaneous catalytic reactions for water splitting (screen 3), and efficient separation of photogenerated electrons and holes (proof). Finally, we successfully identify 1 heterojunction from the pool of 222 items as an efficient photocatalyst for overall solar water splitting. Clearly, this kind of data-driven screening procedure, based on a COF heterojunction database, opens up new avenues and inspires the development of high-performance photocatalysts.

Temperature impact on the morphological evolution of nitrogen-doped carbon quantum dot-decorated zinc oxide and its influence on highly efficient visible-light photocatalyst

Nitrogen-doped carbon quantum dot-decorated zinc oxide (ZnO/NCQD) was synthesized using a hydrothermal process under various thermal conditions. XRD (X-Ray Diffractometer) and field emission-scanning electron microscopy (FE-SEM) confirmed the crystal structure of wurtzite, and there was a morphological evolution from a hexagonal nanorod to a nanoflower. Simultaneously, the optical properties and photocatalytic activity were investigated using UV–visible diffuse reflectance, photoluminescence, and UV–vis spectrophotometers. The presence of NCQD on the ZnO surface lowers the bandgap energy and shifts the absorbance toward visible light. As a result, it enhanced the photocatalytic activity and efficiency of ZnO/NCQD, achieving approximately 80% methylene blue (MB) degradation in 15 min under visible light. It was concluded that the hydrothermal temperature played a role in the particle growth of the ZnO/NCQD and affected the optical and photocatalytic properties. Therefore, the fabricated ZnO/NCQD has excellent potential for photocatalytic dye degradation.

Fe3O4 nanoparticle anchored BiOCl platelet as a highly efficient and reusable visible light photocatalyst

Fe3O4 nanoparticle anchored BiOCl platelet as a highly efficient and reusable visible light photocatalyst

Mesoporous Dual-Semiconductor ZnS/CdS Nanocomposites as Efficient Visible Light Photocatalysts for Hydrogen Generation.

The development of functional catalysts for the photogeneration of hydrogen (H2) via water-splitting is crucial in the pursuit of sustainable energy solutions. To that end, metal-sulfide semiconductors, such as CdS and ZnS, can play a significant role in the process due to their interesting optoelectronic and catalytic properties. However, inefficient charge-carrier dissociation and poor photochemical stability remain significant limitations to photocatalytic efficiency. Herein, dual-semiconductor nanocomposites of ZnS/CdS nanocrystal assemblies (NCAs) are developed as efficient visible light photocatalysts for H2 generation. The resultant materials, synthesized via a polymer-templated self-polymerization method, comprise a unique combination of ~5-7 nm-sized metal-sulfide nanoparticles that are interlinked to form a 3D open-pore structure with large internal surface area (up to 285 m2 g-1) and uniform pores (circa 6-7 nm). By adjusting the ratio of constituent nanoparticles, the optimized ZnS/CdS catalyst with 50 wt.% ZnS content demonstrates a remarkable stability and visible light H2-evolution activity (~29 mmol g-1 h-1 mass activity) with an apparent quantum yield (AQY) of 60% at 420 nm. Photocatalytic evaluation experiments combined with electrochemical and spectroscopic studies suggest that the superior photocatalytic performance of these materials stems from the accessible 3D open-pore structure and the efficient defect-mediated charge transfer mechanism at the ZnS/CdS nanointerfaces. Overall, this work provides a new perspective for designing functional and stable photocatalytic materials for sustainable H2 production.

Synthesis of TiO2 nanotubes from ilmenite with CuS nanoparticles as efficient visible-light photocatalyst.

Titanium dioxide nanotube (TNT) is one of the most widely used photocatalysts. In this research, TNT was prepared by a facile method using ilmenite (FeTiO3) concentrate as the titanium source. For this purpose, iron was leached out from ilmenite using HCl in assistance with the iron powder as the reducing agent to produce pure TiO2, where consequently, TNT was produced through hydrothermal treatment of the prepared TiO2 in an alkaline solution. CuS quantum dots, using the L-cysteine as a linker, were coated on the TNT to improve TNTs' photocatalytic properties. Characterization was done using XRD, SEM, FESEM, HRTEM, FT-IR, nitrogen sorption, and band gap measurement. The results revealed the formation of TNT with a star-shaped macrostructure as well as, a good dispersion of uniform CuS quantum dots with an average diameter of a few nanometers on the TiO2 structure. A dye adsorption kinetics study of the TNT and CuS-dopped TNT showed that TNT carries a higher adsorption capacity compared to the CuS-dopped TNT, developed due to its higher surface area and pore volume. Next, the photocatalytic performance (under visible light) of the prepared composite was studied over the methylene blue (MB) and malachite green (MG) dyes, after the determination of the dye adsorption equilibrium point (where the adsorption stops). TNT showed almost no dye degradation while the prepared composite degraded almost 95 % of the dyes as the result of the reduced band gap from 3.21 to 2.67 eV. In this study, for the first time, the TNT was prepared using a mineral source and ilmenite, enhanced in photocatalytic properties, and presented a successful application.

Au nanoparticles dispersed chitosan/ZnO ternary nanocomposite as a highly efficient and reusable visible light photocatalyst

The environmental pollution in particular contamination of surrounding and ground water are major concerns for regulation authorities and scientific community. In the current work, a novel visible light ternary photocatalytic structure based on mesoporous ZnO in combination with chitosan (CSN) and gold nanoparticles (AuNPs) was synthesized for serious water pollution issue. The Au@CSN/ZnO nanocomposite photocatalyst was developed through the sol-gel methodology followed by ultrasonication and photoreduction techniques. XRD investigation revealed the hexagonal wurtzite structure of ZnO, while XPS and FTIR measurements confirmed the formation of ternary nanocomposite among Au, CSN and ZnO. TEM analysis revealed the presence of AuNPs (5–15 nm), CSN sheets (micron size) and ZnO nanoparticles (20–120 nm) in designed ternary photocatalyst. Diffuse reflectance spectroscopy showed lowering in band gap energy from 3.1 to 2.87 eV as bare ZnO modified to Au@CSN/ZnO. The as-fabricated Au@CSN/ZnO nanocomposite was proven as a decidedly efficient photocatalyst when employed on colorless insecticide imidacloprid (IMD) and on colored methylene blue (MB) dye under visible-light illumination. Efficient photocatalytic performance with 93.21% removal of insecticide only in 20 min was achieved, representing 211% more efficient than bare mesoporous ZnO. In addition, Au@CSN/ZnO nanostructure showed rapid removal of MB with almost complete destruction of complicated structure just in 12 min under visible light. Furthermore, the current-developed photocatalyst exhibited adequate stability and recyclability, which is beneficial for the practical application in environmental remediation.