Bare Photocatalyst Research Articles

Mechanistic insights into the reaction pathway for efficient cationic dye photocatalytic degradation and the importance of the enhanced charge isolation over dual Z-scheme CeO2/BiOCl/Ag2WO4 photocatalyst

Fabricating a multi-component heterojunction system with enhanced charge isolation efficacy remains challenging. A photoactive CeO2/BiOCl/Ag2WO4 heterojunction was successfully constructed using a co-precipitation technique to degrade crystal violet and methylene blue dyes. It was found through a combination of characterization and experiments that the dual Z-scheme system not only augmented the charge isolation and migration efficiency but also maintained superior redox ability with extended visible light absorption capacity. In the CeO2/BiOCl/Ag2WO4 system, 97 % of methylene blue and 98 % of crystal violet were degraded in 75 min using 50 mg/L of ternary photocatalyst. The rate of reaction of CeO2/BiOCl/Ag2WO4 for methylene blue (0.0445 min−1) and crystal violet (0.05053 min−1) exhibited a multi-fold increase in comparison to the bare photocatalysts. The electron spin resonance (ESR) analysis has remarkably identified hydroxyl and superoxide radicals (•OH, •O2−) as the primary reactive species in the photodegradation process. Liquid chromatography-mass spectrometry analysis was utilized to obtain potential degradation pathways for methylene blue and crystal violet, respectively. The dual charge transferal mechanism by the ternary photocatalyst resulted in a significant increase in photocatalytic activity. It provided new perspectives on the principles guiding the rational development of a multicomponent system for environmental remediation.

Effective inhibition of chloride ion interference in photocatalytic process by negatively charged molecularly imprinted photocatalyst: Behavior and mechanism

The ubiquitous chloride ions (Cl−) in water seriously interfere with pollutant oxidation and inevitably generate undesirable chlorinated byproducts. In this study, we report for the first time that a negatively charged molecularly imprinted photocatalyst (MIP) can effectively inhibit Cl− interference and suppress the production of chlorination byproducts (the yield of chloroacetic acid was only 16 % of the bare photocatalyst system) while ensuring efficient degradation of target pollutants, thereby greatly improving the safety of the pollutant degradation process. Taking antibiotics as target pollutant, we investigated the mechanism of action of MIP by comparing the antibiotic degradation pathways, fate of photogenerated active species and production of reactive chlorine species (RCS) in the MIP and bare photocatalyst system. The mechanism by which MIP inhibits Cl− interference was mainly based on a synergy between electrostatic repulsion and steric hindrance induced by the specific capture of antibiotics in imprinted cavity, which effectively suppressed the production of RCS and hindered the participation of RCS in antibiotics degradation. In addition, MIP showed good compatibility with common cations, anions and organic matter, and performed well within a broad pH range in various water environments. Thus, the negatively charged MIP provides a feasible approach for the safe and efficient removal of pollutants in Cl− containing water.

Construction of novel BiOI/CuInS2/ZnO dual S-scheme charge transfer pathway for efficient antibiotic degradation

The present work explored the photocatalytic activity of BiOI–CuInS2–ZnO ternary heterojunction for the photodegradation of the tetracycline (TCl). The bare photocatalysts were prepared via hydrothermal method while the ternary heterojunction was synthesized using simple physical mixing route. The ternary heterojunction of BiOI, CuInS2 and ZnO followed the S-scheme charge transfer pathway exhibiting superior photodegradation ability compared to other synthesized photocatalysts. The attained degradation efficiency of BiOI–CuInS2–ZnO S-scheme ternary heterojunction was 96.75 % within 90 min of light illumination which was much higher than other photocatalysts. Electron spin resonance (ESR) investigations and scavenging experiment indicated that •O2−, and •OH radicals plays an important role in photodegradation of TCl. Furthermore, the structural analysis of synthesized bare photocatalysts was also done via density functional theory (DFT) calculations. The results showed that after the formation of S-scheme heterojunction, the ternary heterojunction showed lower recombination rate (validated via PL analysis) with boosted charge carriers separation rate (confirmed through EIS and TPR analysis) and light absorption ability. This had led to upgradation in photodegradation efficiency of ternary BiOI–CuInS2–ZnO photocatalyst. The reusability test of the photocatalysts confirmed excellent stability of ternary photocatalysts with 90.25 % degradation rate up to five catalytic cycles.

In-situ hydrothermal synthesis of MoS2 /TiO2 nanocomposites for enhanced and stable photocatalytic performance: Methylene blue degradation pathway and mechanism

BackgroundIn recent years, nanocomposite photocatalytic has become more and more attractive and important since it has a great potential to contribute to such wastewater treatment and environmental problems. Pollutant dyes such as methylene blue (MB) have utilizations in manufacturing, paper, medicine and textiles. In addition, creating a Z-scheme nanocomposite illustrates a fitting approach for improving the photocatalytic performance of photocatalysts. Mott-Schottky curves demonstrate that MoS2 and TiO2 are combined to form Z-scheme nanocomposite. MethodsNovel MoS2/TiO2 nanocomposite photocatalysts were well synthesized by a simple hydrothermal process. The photodegradation intermediate products of MB dye are also identified by liquid chromatography-mass spectrometry (LC-MS) and the possible degradation pathway is proposed. Ultimately, the potential photocatalytic pathway mechanism of nanocomposites was verified according to the LC-MS analysis and trapping experiments. Significant findingsThe construction of a Z-scheme nanocomposite is a crucial factor in improving the photocatalytic activity of heterojunction photocatalysts. MoS2/TiO2 nanocomposites had photocatalytic activity within 120 min irradiation to visible light and achieved 98.5 % of MB. A stable heterostructure has been effort designed using MoS2/TiO2 with improved electron and hole migration. The photodegradation performance for MoS2/TiO2 is 3.8 folds that the bare photocatalysts. This nano-heterojunction significantly suppresses the recombination rate of photoexcited charge carriers and enhances the operation of solar energy. The Z-scheme nano-heterojunctions offer a potential strategy for promoting the utilization of photocatalysts in waste environmental purification and clean water.

Fabrication and characterization of ternary composite MgFe2O4/MoO3@CNTs for the enhanced photocatalytic activity to degrade organic pollutants

The recent industrial revolution and population growth have escalated the threat to the environment. Industries themselves discharge millions of tons of different harmful solvents, chemicals, and organic/metal ions into the water system each year. For the degradation of these organic wastes, photocatalysis has been extensively studied. The most researched classes of nanoparticles used as photocatalysts in environmental remediation are metal oxide and metal ferrite nanostructures. In this context, we have fabricated magnesium ferrite (MgFe2O4) nanoparticles and molybdenum trioxide (MoO3) nanorods by coprecipitation and hydrothermal processes, respectively. Moreover, their binary composite (MgFe2O4/ MoO3) was fabricated to improve the absorption of light in the visible region. Further, its ternary composite was fabricated with CNTs (MgFe2O4/MoO3 @CNT) to enhance photocatalytic activity by reducing the recombination rate via trapping photoinduced species. X-rays diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic analysis were carried out for structural confirmation. From XRD data, the crystallite size and other crystallographic parameters of the fabricated samples were determined. The calculated crystallite sizes of MgFe2O4 and MoO3were 12.74 nm and 31.36 nm, respectively. Band gap calculation and optical studies were done by UV–visible spectroscopy. The decrease in band gap value of MgFe2O4/MoO3 leads to remarkable photocatalytic activity than bare photocatalysts. The photocatalytic performance of all photocatalysts was examined by degrading methyl orange (MO) dye, pendimethalin (PDM), and benzoic acid (BA). Comparative studies revealed that MgFe2O4/MoO3 @CNT exhibited brilliant photocatalytic activity among the aforementioned photocatalysts. It degraded 96%, 82%, and 67% methyl orange (MO), pendimethalin (PDM), and benzoic acid (BA), respectively. This outstanding increase in photodegradation process was due to the movement of photoexcited species from the conduction band to CNTs, where it traps the photoexcited species and limits their chances of recombination. Overall, this research offers a fresh understanding of the effective utilization of the MgFe2O4/MoO3 @CNT ternary composite as a high-performance photocatalyst to address environmental protection concerns when exposed to visible light.

Defective cobalt and copper tungstates mixtures with TiO2 for photocatalytic CO2 reduction

In this work, the application of highly defective cobalt and copper tungstates was proposed for photocatalytic CO2 reduction. The materials were synthesized by hydrothermal method and characterized with SEM, EDS, XRD, XPS and DRS techniques. Studied materials were examined in photocatalytic CO2 reduction to CO in the gas phase, as bare photocatalysts and in mixtures with TiO2. The behavior of the junctions between the mixture components was determined using photoelectrochemical, spectroelectrochemical and surface photovoltage measurements. These studies reveal different types of junctions for the synthesized materials (disturbed S-scheme for CoT/TiO2 and type-I for CuT/TiO2). It was found the CuT/TiO2 mixture is more effective than CoT/TiO2 due to lower recombination rates of photogenerated charge carriers and the presence of a larger number of W5+ and Cu2+ active centers.

Photodegradation of ceftriaxone using g-C3N4-ZnO nanocomposite as an efficient photocatalyst

The entrance of emerging contaminants (ECs) (hormones, dyes, pesticides, pharmaceuticals, etc.) into natural waters threatens public health and the ecosystem due to their longer half-life and low biodegradability. Particular interest is placed on antibiotics, whose presence in aqueous systems notoriously increased the recent COVID-19 pandemic and, thus, the risk for various organisms and other collateral implications. This work evaluates the photocatalytic activity of graphitic carbon nitride (g-C3N4)-zinc oxide (ZnO) composites (CNZO), compared to bare photocatalytic materials, to degrade Ceftriaxone (CEF) antibiotic. The synthesis methodology of materials comprised the obtention of bare photocatalysts using hydrothermal (ZnO) and thermal polymerization (g-C3N4) methods, whereas, for CNZO composites, wet impregnation methodology was employed. The impact of g-C3N4 wt% content (10, 25, 50, and 75%) in composites was investigated by correlating variations in their structural, morphological, chemical, and optical properties with their photocatalytic activity under UV and visible irradiation. The results showed an optimal relation between ZnO and g-C3N4 wt% content (CNZO (25–75) sample), resulting in complete molecule degradation in 60 min and 93 % of degradation in 180 min under UV and visible radiation, respectively. The reusability of the CNZO (25–75) sample was tested in five consecutive ceftriaxone-degradation cycles, where no deactivation phenomena in the sample (92% of degradation) was observed, suggesting its good stability and potential application in practical experiments. The enhanced photocatalytic activity is attributed to decreasing recombination of the charge carriers evidenced by PL spectra, which confirms the heterojunction formation between ZnO and g-C3N4. Based on the results, a schematic photocatalytic mechanism was proposed, which describes the enhanced electron-hole separation at the materials interface. These results provide a guideline for obtaining composites with superior photocatalytic activity. Additionally, their visible light-active feature might be helpful towards the use of sunlight, overcoming conventional photocatalysts (ZnO, TiO2, etc.) drawbacks.

Biomass-derived activated carbon nanocomposites for cleaner production: A review on aspects of photocatalytic pollutant degradation

Nowadays, water contamination resulting from the disposal of industrial and urban waste poses a significant threat to marine life and human. Hence, providing an effective treatment approach to reduce the total cost and duration of the wastewater treatment process is crucial. Although the adsorption and photocatalysis methods show superb potential for removing hazardous pollutants from water, their combination through a suitable synthesis route is one of the most effective ways to overcome their limitations. Activated carbon (AC) significantly accelerates the rate of pollutant degradation for AC-based photocatalysts compared to bare photocatalysts because of its ability to increase the number of attachment sites, strengthen the interaction between pollutants and photocatalysts, and facilitate rapid electron transfer to prevent electron or hole recombination. This study aims to investigate four main objectives: 1) evaluating key parameters to enhance the surface characterization of AC-derived from lignocellulosic sources using physical and chemical techniques; 2) Surveying various approaches for synthesizing AC-based photocatalysts; 3) explaining the mechanism of photocatalytic degradation of pollutants and the operating parameters in the wastewater treatment process; and 4) providing an overview of the opportunities, challenges, suggestions, and potential future outlooks. Future studies should focus on understanding the structural properties of AC to design effective photocatalytic systems for degrading hazardous contaminants. Generally, AC-based nanocomposites reduce both process costs and duration and promote environmental sustainability by effectively eliminating pollutants.

Novel Type-II Heterojunction Binary Composite (CdS/AgI) with Outstanding Visible Light-Driven Photocatalytic Performances toward Methyl Orange and Tetracycline Hydrochloride.

In this study, an effective type-II heterojunction CdS/AgI binary composite was constructed by an in situ precipitation approach. To validate the successful formation of heterojunction between AgI and CdS photocatalysts, the synthesized binary composites were characterized by various analytical techniques. UV-vis diffuse-reflectance spectroscopy (UV-vis DRS) revealed that heterojunction formation led to a red shift in the absorbance spectra of the CdS/AgI binary composite. The optimized 20AgI/CdS binary composite showed a least intense photoluminescence (PL) peak indicating highly improved charge carrier (e-/h+ pairs) separation efficiency. The photocatalytic efficiency of the synthesized materials was assessed based on the degradation of methyl orange (MO) and tetracycline hydrochloride (TCH) in the presence of visible light. Compared to bare photocatalysts and other binary composites, the 20AgI/CdS binary composite showed the highest photocatalytic degradation performances. Additionally, the trapping studies showed that superoxide radical anion (O2•-) was the most dominant active species involved in photodegradation processes. Based on the results of active species trapping studies, a mechanism was proposed to describe the formation of type-II heterojunctions for CdS/AgI binary composite. Overall, the synthesized binary composite has tremendous promise for environmental remediation due to its straightforward synthesis approach and excellent photocatalytic efficacy.

Carbon composites for rapid and effective photodegradation of 4-halogenophenols: characterization, removal performance, and computational studies

The research deals with the facile ultrasound-assisted in situ sol–gel synthesis of composites of titania and granular activated carbon targeting for the efficient and fast photocatalytic removal of 4-halogenophenols (4-HPhs), which possess an adverse effect to humans and ecosystem health. The combination of state of art analytical techniques, such as TEM, BET, XRD, XPS, IR, and DRS revealed the potentially useful photocatalytic properties of synthesized materials based on the availability of titania polymorphs and the contribution of high surface area of activated carbon. Removal efficiency of all composites towards a variety of 4-HPhs was really high (up to 99.9 %) and rapid (1 h). The degradation rate of composite materials was higher than for bare photocatalysts that can be interpreted by the presence of additional elimination forces, mainly, the adsorption on activated carbon. XPS studies of the materials after photocatalysis showed their potential in cyclic usage. The DFT modelling revealed the formation of strong (H-bonds) and weak van der Waals interactions between 4-chlorophenol (4-CPh) and the synthesized materials. The ALIE minima have indicated the most reactive sites in 4-CPh molecule, which were under attack during photocatalysis. The present study proposes the materials with self-cleaning properties to be utilized in chemical pollution treatment.

A Z-scheme photocatalysis for phenol eradication from water using peroxymonosulfate activation Ag/AgBr/SCN nanocomposite

BackgroundThe present work was mainly focused on construction of direct Z-scheme Ag/AgBr/SCN heterostructure and their photocatalytic ability to removal of phenol using synthesized photocatalysts. Ag/AgBr/SCN photocatalyst was prepared via facile deposition-precipitation method while bare g-C3N4 (GCN) and SCN (sulphur doped g-C3N4) were prepared via simple thermal-polycondensation method. MethodsThe Ag/AgBr/SCN Z-scheme heterostructure was fabricated by integration of 2D SCN with AgBr. Doping of sulphur in GCN structure has incremented the light absorption ability of GCN via reducing the energy gap to 2.64 eV from 2.7 eV. Different spectroscopic and analytical techniques have confirmed the successful formation of photocatalysts. Significant findingsThe addition of PMS during the photocatalytic experiment has enhanced the removal efficiency of photocatalysts due to more •OH and •SO4−radicals generation. It was observed from the results that PMS assisted Ag/AgBr/SCN photocatalytic material exhibited highest removal efficiency i.e. 99% compared to other bare photocatalysts within 80 min of visible-light exposure. Proposed mechanism validated the Z-scheme charge transfer route in Ag/AgBr/SCN in accord to apt band alignment in SCN and AgBr. However, Ag metal acted as an electron mediator to just transfer the electron from CB of SCN to CB of AgBr. The transference of electron from sulphur doped g-C3N4 to AgBr through Ag improved electron transportation. This ultimately enhanced charge separation rate and reduced the charge recombination rate in Ag/AgBr/SCN nanocomposite. The proposed mechanism also presented that •OH, SO4•− and •O2− radicals were the primary reactive species during Ag/AgBr/SCN/PMS assisted photocatalytic phenol degradation process (verified through scavenging tests). Finally, the recyclability experiment confirmed the stability and reusability of the prepared photocatalyst to 5 consecutive cycles. Consequently, this work presents a new perspective to fabricate greener, cheaper and proficient visible driven photocatalytic material for wastewater detoxification and environmental remediation.

Quantum Dot-Embedded Hybrid Photocatalytic Nanoreactors for Visible Light Photocatalysis and Dye Degradation

Utilization of visible light to drive chemical transformations is a fascinating field of research and particularly important in the current socioeconomic context. However, bare photocatalysts often undergo photodegradation or agglomeration, which limits their recyclability. In this regard, designing robust and flexible artificial photocatalytic nanoreactors with embedded catalytic units finds tremendous importance in recent times. Herein, we utilized quantum dot (QD)-embedded coacervate nanodroplets (NDs) as photocatalytic nanoreactors for model chemical transformations, which are otherwise inefficient with bare QDs in bulk aqueous solution. Hybrid NDs fabricated from negatively charged CdTe QDs and positively charged poly(diallyldimethyl) ammonium chloride (PDADMAC) have been exploited as a confined host toward efficient visible light-driven photoredox transformation of ferricyanide (Fe3+) to ferrocyanide (Fe2+) and photocatalytic dye degradation of rhodamine B and methylene blue. The present NDs display excellent recyclability without any appreciable decrease in the conversion yield and reaction kinetics. Our findings suggest the involvement of individual QDs embedded within these NDs as the active photocatalytic site for these transformations. The observed photocatalytic activity of the QD-embedded NDs arises due to the combined effect of surface charge modulation of embedded QDs and nanoconfinement inside the nanoreactor. The present study paves the way for designing next-generation photocatalytic nanoreactors toward a vast array of photochemical conversions involving semiconductor nanoparticles.

NiO/CuO/TiO2 Ternary Composites: Development, Physicochemical Characterization and Photocatalytic Degradation Study Over Reactive Orange 30 Solutions Under Solar Light Irradiation

Abstract The photocatalytic degradation and mineralization of Reactive Orange 30 on NiO/CuO/TiO2 ternary composites have been studied using solar light irradiation. The NiO/CuO/TiO2 ternary composites were prepared by producing ethanolic dispersions containing varied amounts of NiO and CuO/TiO2 (3wt% to 15wt.%), followed by annealing at 300 °C. SEM, UV- Vis DRS, PL, XRD and FTIR analysis have been used to characterize the unary (parent photocatalysts), binary and ternary composites. Under solar light irradiation, NiO/CuO/TiO2 ternary composites exhibited an excellent photocatalytic activity in degradation of reactive orange 30 in aqueous solution, whereas the NiO/TiO2, CuO/TiO2 and bare photocatalyst such as NiO, CuO, TiO2 showed lower activities. It was deduced that the remarkable visible-light absorption phenomenon and band gap reduction of the NiO/CuO/TiO2 ternary composites taking place. It paves way for the photogenerated electron transfer between CB of the NiO, CuO, TiO2 semiconductors and also holes shifting between VB of above mentioned materials. The NiO/CuO/TiO2 ternary composite shows good photostability and the photocatalyst retains 94% of its initial activity in the seventh cycle, respectively.

Role of MoS2/rGO co-catalyst to enhance the activity and stability of Cu2O as photocatalyst towards photoelectrochemical water splitting

Solar to hydrogen conversion using photocatalyst is one of the most promising methods to get a pollution free and sustainable fuel. Most of the photocatalysts suffer with major problems like, charge recombination and photocorrosion, which diminishes their practical application. The need is to obtain a stable photocatalyst where the photocorrosion is inhibited. Cu2O has been used as a photocatalyst and it holds promise being non-toxic and abundantly available on earth. However, due to lower band edge of Cu2O, it gets oxidized easily and its high recombination rate of electron-hole pairs which lowers its activity. For the inhibition of the photocorrosion, there is a need of a passivation layer that protects the photocatalyst by blocking the unfavorable reaction which causes photocorrosion. Here, we have used MoS2/rGO as a co-catalyst with Cu2O to suppress the recombination rate of the photogenerated charge carrier in Cu2O as well as to inhibit the photocorrosion and provide an electron rich environment to the system. The ternary composite shows higher photoactivity as compared with the bare one. The photoelectrochemical activity of the bare photocatalyst was 0.33 mA cm−2 while the photoelectrochemical activity of the ternary composite Cu2O-MoS2/rGO was 8.46 mA cm−2 at 0.95 V. Transient photocurrent response measurement provides the stability information of the photocatalysts.

Construction of direct Z-scheme SnS2@ZnIn2S4@kaolinite heterostructure photocatalyst for efficient photocatalytic degradation of tetracycline hydrochloride

The accumulation of antibiotics in water system and the consequent detrimental effects have drawn worldwide attention extensively. There is an urgent need to develop rapid and efficient degradation methods of antibiotics. In this work, a highly efficient SnS2@ZnIn2S4@kaolinite (SZK) photocatalysts were successfully synthesized by hydrothermal method. In comparison with bare photocatalysts, the SnS2@ZnIn2S4@kaolinite (SZK) heterostructure demonstrated greatly improved adsorption-photocatalytic degradation capability for removal of tetracycline hydrochloride (TCH). Under visible light illumination, the apparent reaction rate of SZK heterostructure reached 0.0231 min−1, which was around 20.81 times and 2.37 times higher than that of SnS2 and ZnIn2S4, respectively. It has been proved that •O2− and 1O2 are the main active species participating the degradation process. Based on HPLC-MS analysis, the possible photodegradation pathways of TCH have been proposed. The superior removal performance is mainly ascribed to the enhanced adsorption ability, elevated light harvesting and the increased separation efficiency originated from the synergistic effect of the components. Our study provides new insights with the utilization of natural minerals for visible light photocatalytic degradation of antibiotics in wastewater treatment.

Enormous Promotion of Photocatalytic Activity through the Use of Near-Single Layer Covalent Organic Frameworks

Enormous Promotion of Photocatalytic Activity through the Use of Near-Single Layer Covalent Organic Frameworks

Photocatalytic Hydrogen Evolution Over Pt/Co-TiO2 Photocatalysts

Aims: In this study, the photocatalytic hydrogen evolution reaction from aqueous methanol was investigated upon simulated solar light using platinum loaded on cobalt doped TiO2 (Pt/Co-TiO2) composites. Background: Controversial results of cobalt-based composites create doubts about their photocatalytic activity. Thus, cobalt doped TiO2 composites were synthesized differently, and the photocatalytic activity was examined for the photocatalytic hydrogen generation. Objective: The current study aims to investigate the influence of cobalt doping and platinum loading on the photocatalytic activities of TiO2 nanoparticles for the photocatalytic H2 generation. Methods: The 0.5 wt.% Co-TiO2 and bare TiO2 photocatalysts were synthesized using two different methods, namely, reflux and hydrothermal synthesis. Additionally, the Pt deposition on the prepared Co-TiO2 and TiO2 catalysts (1 wt.% Pt) was performed using a photo-platinization method. : The as-prepared catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy/ energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM), ultraviolet- visible spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and electrochemical impedance spectroscopy (EIS). Result: The XRD and EPR studies clearly indicated that the Co was incorporated into the titanium dioxide lattice. The EIS results suggested that the reduction of protons over Co-TiO2 and bare TiO2 materials was possible from a thermodynamic point of view. However, the photocatalytic results revealed that the formed amount of H2 was extremely low and close to the detection limit. The evolution of H2 from aqueous methanol (10 vol%) showed higher rates when employing 1 wt.% Pt loaded on 0.5 wt.% Co-TiO2 photocatalysts under simulated solar light irradiation. A maximum of 317 ± 44 μmol.h-1 was observed over the Pt/Co-TiO2-HT photocatalyst. Conclusion: EPR results confirmed that the cobalt ions were introduced into the TiO2 lattice by trapping the photogenerated conduction band electrons and decreasing the defects in the crystal cell. The Mott−Schottky analysis of electrochemical impedance measurements showed that all catalysts were ntype semiconductors and that cobalt doping induces impurity level within the band gap of TiO2. The experimental results of photocatalytic H2 generation from methanol-reforming demonstrated that no significant impact of Co-doping on the photocatalytic H2 formation was observed neither for bare TiO2 samples nor for the platinized materials. Based on these experimental findings, a possible mechanism for the continuous photocatalytic activity of Pt/Co-TiO2 photocatalysts under simulated solar light was proposed.

High photoactivity of Bi2O2(CO3)/Zn5(CO3)2(OH)6 prepared by a facile one-pot synthesis for the efficient degradation of phenol under UV light

The synthesis of Bi2O2(CO3)/Zn5(CO3)2(OH)6 heterojunction at low-temperature and template-free synthesis was carried out promoting the growth of sheet-like structures. The novel material has shown a high photocatalytic performance in the phenol removal under UV light when is compared to the Zn5(CO3)2(OH)6 and Bi2O2(CO3) bare photocatalysts. It is worth mentioning that, the material composed by a molar ratio of Bi/Zn = 0.08 showed the highest percentage of phenol mineralization. All the synthesized materials were characterized by X-ray diffraction, infrared spectroscopy with Fourier transform, diffuse reflectance spectroscopy, adsorption-desorption isotherms of N2, X-ray photoelectron spectroscopy, scanning electron microscopy and high-resolution transmission electron microscopy. The addition of Bi2O2(CO3) to the Zn5(CO3)2(OH)6 structure promotes the oxygen vacancies (OV) increment which make slower the recombination process between the e− and h+ species. This is because the OV sites act like a trap of the photogenerated holes. Thus, the photocatalytic activity is enhanced when Zn5(CO3)2(OH)6 is modified by the addition of Bi2O2(CO3) propitiate an increase on the production of hydroxyl and superoxide radicals as oxidant species for the phenol removal. As a novel material, Bi2O2(CO3)/Zn5(CO3)2(OH)6 could potentially be applied as an efficient material for phenol removal in photocatalysis due to the high performance, facile preparation and the synergetic effect achieved by the heterojunction presence.

Efficient visible-light piezophototronic activity of ZnO-Ag8S hybrid for degradation of organic dye molecule

The usage of semiconductor photocatalyst has been received great attention in recent years due to their wide application in photocatalytic water-splitting and degradation of pollutants in waste water and environmental remediation application, etc. In this study, we demonstrated the efficient synergistically piezo-phototronic effect (which is combined activity of piezo- and photocatalytic) of ZnO-Ag8S hybrid for the degradation of an organic dye. Hydrothermal method was adopted for the growth of ZnO tetrapods on the surface of glass substrate. Ag8S modified ZnO obtained by successive ionic layer adsorption and reaction (SILAR) method, has shown an increased photo-decolorization rate compared with bare photocatalyst. This piezo-photocatalytic hybrid material plays an important role in electron trapping and also hindered the charge carrier recombination. The photo-degradation mechanism of Rhodamine-B dye with Ag8S modified piezoelectric ZnO hybrid material has shown 7.3 fold increment when compared with bare photocatalyst. Our study reveals that ZnO-Ag8S hybrid shows a better visible-light piezophototronic activity which further explores a new catalyst design approach for existing photocatalytic application in environmental remediation.

Tailoring charge transport in BaBiO3/NaTaO3 heterojunction interface for enhanced photocatalytic and photoelectrochemical H2 generation

Photoactive perovskites NaTaO3 and BaBiO3 were synthesized by the solid-state method. The resulting compounds were mixed by wet impregnation, adding BaBiO3 (BBO) onto the base material NaTaO3 (NTO) to obtain the compounds X-BBO/NTO (X = 5–30 wt.%). The sample 20-BBO/NTO presented the largest crystallites (135 nm). Since BaBiO3 presents narrower Eg value (≈ 2 eV) than NaTaO3 (≈ 4 eV), the addition of BBO to NTO promoted a better visible light harvesting. This feature can be explained by the formation of a heterojunction, which improves the photocatalytic activity by an abatement of the charge carrier recombination. Photoelectrochemical tests showed an improvement in the charge transfer resistance and enhanced photoelectrocatalytic activity for the 20-BBO/NTO sample, over the other BBO concentrations and bare photocatalysts. An optimal amount of BaBiO3 (20 wt.%) increased the synergy of the n-type heterojunction by an enhancement in the charge transfer processes to perform the photoelectrocatalytic water splitting. 20-BBO/NTO sample showed the highest hydrogen production of 54 μmol g−1, which outstripped 1.4 times the photocatalytic hydrogen generation of the bare NaTaO3 semiconductor.