Semiconductor Photocatalytic Materials Research Articles

Synthesizing pyridinic-N dominate-doped graphene/BiVO4 nanocomposite as a superior photocatalyst for degradation under visible-irradiation

Abstract The disadvantage of bismuth vanadate (BiVO4), a metal oxide semiconductor photocatalytic material, can be overcome by constructing nitrogen-doped graphene-based nanocomposites. Here we state to synthesis pyridinic-N doped graphene/BiVO4 nanocomposite (N-rGO/BiVO4). Because of many defects were existed pyridinic N-rGO, more tiny particle size and interaction from abundant interfacial, between BiVO4 and N-rGO sheets, can produce synergistic effects and enhance photocatalytic performance. N-rGO/BiVO4 composite has a large light absorption range and high photocatalytic activity compared with BiVO4 and rGO/BiVO4. XPS, PXRD, HRTEM, FESEM, UV–vis, PL. etc analytical methods are used to characterize samples and the change of bandgap of samples is verified through theoretical analysis and simulation. After photocatalytic testing, the decomposition of methylene blue dye just required only 80 min under visible light and photocatalytic degradation efficiency of 99.3%. N-rGO/BiVO4 has great potential for the removal of refractory pollutants from wastewater.

Development of novel BiOBr0.75I0.25 nanostructures with remarkably High dark phase bactericidal activities

Semiconductor materials with promising photocatalytic activities are being developed for numerous applications including their use in the development of antibacterial products. However, the light may not be available everywhere, which restrict the use of semiconductor photocatalytic materials in real applications. In this area, we report a novel nanostructure of BiOBr0.75I0.25 to show enormously high bactericidal activities even at dark. We used a solution based single step method at room temperature to produce highly porous and crystalline BiOBrxI1-x (x = 0–1) nanostructures. Next, the developed materials were thoroughly characterized by different analytical techniques, such as FESEM, XRD, XPS, etc. To evaluate the bactericidal activities Escherichia coli (gram-negative bacteria) and Bacillus subtilis (gram-positive bacteria) were selected. Interestingly we found that the solid solutions exhibited high potential towards both the bacteria and among them, BiOBr0.75I0.25 showed extremely high efficiencies even at dark. Due to their semiconductor behavior, the materials have shown higher activities in the presence of any light source. The knowledge about the behavior of these unique materials revels a new area of research and would certainly help to find out the solution for ever-increasing environmental issues.

Chemically synthesized (Ag, Mn2O3)-codecorated ZnO nanoparticles for achieving superior visible light-induced photodegradation and enhanced gas sensing activity.

Heterostructural engineering and noble metal coupling are effective strategies to optimize semiconductor photocatalytic materials. In this work, (Ag, Mn2O3)-codecorated ZnO nanoparticles with different Mn2O3 contents (0-10 mol%) were synthesized by integrating the two strategies by a facile two-step polymer network-gel process. The photocatalytic activity of Ag/ZnO (AZM0) was significantly enhanced with the optimum Mn2O3 molar ratio of 3 mol%. The degradation efficiency of AZM3 is ∼3 times and ∼4.8 times higher than that of AZM0 for the degradation of methylene blue (MB) upon exposure to simulated sunlight and visible light, respectively. Also, this ternary nanocomposite exhibits enhanced gas sensing performance towards NO2 under ultraviolet/visible light irradiation at room temperature. The analysis of its microstructural, optical and photoelectrical characteristics suggests the synergistic coupling effects of Ag and Mn2O3, in which the significantly enhanced visible light response and hetero-interface charge carrier migration are the critical factors for the improvement of photocatalytic efficiency and gas sensing activity. Furthermore, the effects of recycling ability, the influence of the initial solution pH, the catalyst dosage and the main active species during the catalysis process on photocatalytic activity were explored. This study develops a feasible pathway to consciously construct multiheterostructures for enhancing the photocatalytic activity with great potential applications in toxic pollution abatement and noxious gas detection.

G-C3N4 composited TiO2 nanofibers were prepared by high voltage electrostatic spinning to improve photocatalytic efficiency

Semiconductor photocatalysis technology is one of the ways to control environmental pollution using solar energy. Because of its chemical stability, low toxicity and high photocatalytic oxidation-reduction ability, titanium dioxide has become one of the most widely studied and applied semiconductor photocatalytic materials. However, there are also some problems such as the response only in the ultraviolet range, rapid recombination of electron pairs produced by light during photodegradation, and the small specific surface area. On account of the limitations of titanium dioxide photocatalyst, the key factors and breakthroughs to improve performance new materials, this paper uses g-C3N4 of improving the photocatalytic function of titanium dioxide. Because g-C3N4 has good conductivity, relatively strong adsorption capacity and larger specific surface area compared with other carriers, g-C3N4 is one of the most promising carriers. In this research work, g-C3N4/TiO2 heterogeneous nanocomposites were prepared by combining TiO2 nanowires with g-C3N4. First of all, we need to change the morphology of titanium dioxide. We use high-voltage electrospinning technology to achieve this goal. This method greatly increases the specific surface area and increases the active sites involved in photocatalytic activity. Then, g-C3N4 was prepared with melamine as raw material by high temperature calcination. Then, the hydrothermal method combined with the good characteristics of g-C3N4 enhanced the deflection of photogenerated electrons and prolongs the lifetime of photogenerated electron-hole pairs. The photocatalytic efficiency of nanocomposites is greatly improved Rhodamine B solution was completely degraded in 120 min.

Electronic and optical properties of Zn-S, Ag-C, Ag-N and Ag-S co-doped K2Ti6O13 with different doping concentrations

K2Ti6O13 is a wide band gap semiconductor photocatalytic material. Its absorption spectrum is concentrated in the ultraviolet band, which limits its application as a photocatalyst. Doping can effectively improve its light absorption. Based on the first principles and the density functional theory, crystallographic properties, electronic properties and optical properties of pure K2Ti6O13 and of Zn-S, Ag-C, Ag-N and Ag-S co-doped K2Ti6O13 with different doping concentrations have been calculated and compared. The results show that K2Ti4Ag2O12N (Ag’s doping concentration is 33.33 % and that of N is 7.69 %) has the best absorption capacity of visible light. This study provides a valuable theoretical reference for the application and preparation of potassium titanate photocatalyst materials. Certain doping concentrations and doping atoms can be selected according to different needs to prepare potassium titanate with specific characteristics.

Defective ultra-thin two-dimensional g-C3N4 photocatalyst for enhanced photocatalytic H2 evolution activity

The two-dimensional semiconductor photocatalytic material has excellent photocatalytic H2 evolution activity. In order to further improve the hydrogen production activity of g-C3N4, this study improved the preparation process of g-C3N4 and obtained a new photocatalyst (name H-CN) with a higher absorption range, larger specific surface area, and faster hydrogen production activity. Compared with the originally prepared g-C3N4, the H-CN absorption range has been improved, and the utilization of visible light has reached 650 nm. When the doping amount of Pt cocatalyst was 1.0 wt%, the H-CN demonstrates excellent photocatalytic hydrogen production activity, with a hydrogen production rate of 4.3 mmol h−1·g−1, which was 7.0 times higher than that pure 1.0 wt% Pt/g-C3N4. The fluorescence spectroscopy of H-CN showed better separation of carriers and longer lifetime. This study has guiding significance for the preparation of subsequent ultra-thin nanosheet photocatalysts and the establishment of high-efficiency photocatalytic systems.

Recent Developments of Advanced Ti3+-Self-Doped TiO2 for Efficient Visible-Light-Driven Photocatalysis

Research into the development of efficient semiconductor photocatalytic materials is a promising approach to solving environmental and energy problems worldwide. Among these materials, TiO2 photocatalysts are one of the most commonly used due to their efficient photoactivity, high stability, low cost and environmental friendliness. However, since the UV content of sunlight is less than 5%, the development of visible light-activated TiO2-based photocatalysts is essential to increase the solar energy efficiency. Here, we review recent works on advanced visible light-activated Ti3+-self-doped TiO2 (Ti3+–TiO2) photocatalysts with improved electronic band structures for efficient charge separation. We analyze the different methods used to produce Ti3+–TiO2 photocatalysts, where Ti3+ with a high oxygen defect density can be used for energy production from visible light. We categorize advanced modifications in electronic states of Ti3+–TiO2 by improving their photocatalytic activity. Ti3+–TiO2 photocatalysts with large charge separation and low recombination of photogenerated electrons and holes can be practically applied for energy conversion and advanced oxidation processes in natural environments and deserve significant attention.

Enhanced photocatalytic activity and hydrogen evolution of CdS nanoparticles through Er doping

Generation of hydrogen fuel via the photocatalytic water splitting mechanism using semiconductor nanoparticles under sunlight irradiation is highly important. Moreover, the development of nanophotocatalysts for polluted water treatment is significant. In this regard, we synthesized CdS, CdS:Er (2 at%), and CdS:Er (4 at%) nanoparticles by a simple reflux route. According to the comprehensive structural analysis, Er3+ ions were incorporated into the CdS host lattice at the substitutional and interstitial sites, without altering the original structure. Photocatalytic measurements revealed that the degradation efficiency of 2 at% Er-doped CdS nanoparticles reached 100% within 100 min of visible light irradiation. In addition, CdS:Er (2 at%) nanoparticles exhibited enhanced photocatalytic hydrogen generation ability under simulated sunlight irradiation. Hence, from the obtained results, we concluded that CdS:Er (2 at%) nanoparticles are promising semiconductor photocatalytic materials for wastewater treatment as well as hydrogen fuel generation.

Application of Photocatalytic Materials in Sensors

AbstractPhotocatalysis technology can not only decompose water, toxic and harmful substances in the environment, but also directly convert solar energy into electricity and other clean energy. Therefore, the application of photocatalytic materials in sensors has great potential. The purpose of this paper is to review and discuss the application and potential of photocatalytic materials in sensors. The content includes the application of various photocatalytic materials in sensors. The photocatalytic materials mainly include n‐type semiconductor materials TiO2, ZnO, SnO2, Fe2O3, WO3, In2O3 and nonmetallic semiconductor C3N4. Sensors include gas sensors, photoelectrochemical sensors, electrochemical sensors, photocatalytic sensors, and other sensors. The results show that photocatalytic materials are most widely used in gas sensors. In addition to using photocatalytic materials to detect gas, the most common method is to use photocatalytic materials to detect the concentration of metal ions and organic substances in water. The most widely used photocatalytic material is titanium dioxide, and C3N4 as a nonmetallic semiconductor is rarely used in sensors. It can be concluded that photocatalytic materials have great potential in the application of sensors, among which C3N4 as a nonmetallic semiconductor photocatalytic material has more potential.

Efficient formaldehyde photo-oxidation and reaction path study on oxygen vacancy engineered TiO<sub>2</sub>

<p indent=0mm>With the intemperate depletion of energy resources and the ever-increasing emission of volatile organic compounds (VOCs), environmental issues will suffer even further. As a main contributor of VOCs, formaldehyde is quite volatile and poisonous. Short-term exposure to an environment that exceeds the standard concentration of formaldehyde (>0.1 mg/m³) would result in nausea, chest distress and headaches. While long-term exposure to formaldehyde concentrations in excess of the environmental standard can lead to lung cancer, pancreatic cancer, leukemia and even teratogenic effects. Therefore, researchers have been anchored their hopes on the complete conversion of formaldehyde into nontoxic and harmless compounds, such as CO₂ and H₂O. The traditional methods for removing formaldehyde from the environment include condensation, biological treatment and physical adsorption. However, these methods have problems with secondary pollutants and exhibit poor remediation performance at low concentrations of formaldehyde (ppm levels, namely, <sc>1 ppm=1</sc> mg/m³). Photocatalytic oxidation is an efficient green technology that can absorb the photons in sunlight by utilizing semiconductor photocatalytic materials. When the photon energy is higher than or equal to the semiconductor band gap (<italic>E</italic>_g), electrons can be transferred to the conduction band and left holes in the valence band. These photo-induced carriers, composed of photo-excited electrons and holes, can effectively trigger redox reactions that accomplish the removal of target pollutants. Along with the seminal report by Fujishima describing photocatalytic water splitting to produce hydrogen by employing TiO₂ in 1972, interests are emerging in the development of TiO₂-driven pollutant treatment. TiO₂ is a typical photocatalytic semiconductor that is strongly oxidized, non-toxic and chemically stable. However, the photo-aroused electrons in TiO₂ easily recombine with the holes, leading to a low quantum efficiency (<5%). The electron-holes separation rate of a photocatalyst during a photocatalytic process is affected by factors like its phase structure, particle size, crystallinity and specific surface area. Recently, some studies have reported a series of non-stoichiometric photocatalytic semiconductor materials, such as ZnO₁₋_{<italic>x</italic>}, SnO₂₋_{<italic>x</italic>}, BiO₂₋_{<italic>x</italic>} and TiO₂₋_{<italic>x</italic>}. These materials contain a large amount of vacancy defects, which can result in lattice distortion and introduce defect energy levels that accelerate the separation of charge carriers and thus further improve the photocatalytic performance. However, three problems are commonly observed with these reports: (1) The synthetic methods are complex and related to the use of strong acids, strong bases or poisonous and harmful chemicals; (2) the prepared materials cannot effectively degrade low concentrations of formaldehyde; and (3) the mechanisms and reaction paths based on formaldehyde degradation have not been determined. To enhance the photocatalytic behavior and clarify the reaction mechanism and route involved in low concentrations of formaldehyde degradation, in this paper, TiO₂ with surface oxygen vacancy was successfully prepared by calcination of P25 TiO₂ under vacuum condition, and the resulted TiO₂ with oxygen vacancy (O_v-TiO₂) exhibits superior photocatalytic activity towards formaldehyde oxidation in a continuous-flow reactor. The removal rate of formaldehyde over illuminated O_v-TiO₂ reaches 95.05%, which is 1.31 times higher than that of pristine TiO₂ with a formaldehyde removal rate of 72.52%. The experimental results showed that the introduction of O_v can not only extend the light-responsive range, but also facilitate the separation of photo-generated electron-hole pairs, therefore, enhancing the photocatalytic performance of TiO₂. <italic>In-situ</italic> infrared spectroscopy and DFT calculation indicated that the presence of O_v can improve the adsorption and activation of formaldehyde molecules. The rich delocalized electrons at the O_v sites of TiO₂ can migrate to molecular formaldehyde, which then actively fracture the C=O bonds of formaldehyde, sharply diminishing the accumulation of organic intermediates such as formic acid. This study highlights the influence of oxygen vacancies steered TiO₂ on the photo-oxidation reaction process, affording a new idea for the surface vacancy design of photocatalyst and photocatalytic treatment of gaseous pollutants. We see creating this kind of oxygen vacancies engineered TiO₂ with excellent photocatalytic behavior and repeatability can be as the key goal for future application-oriented work.

Constructing defective (BiO)2CO3 with different dominated facets for efficiently photocatalytic NO oxidization and in situ reaction pathway study

Fast electron transfer, slow charge recombination and low visible light absorption always limit semiconductor photocatalytic materials. Hence, we develop a facile (BiO)2CO3 photocatalyst, which possess different dominated facets with oxygen vacancy by one-step hydrothermal synthesis method. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, electron spin resonance, UV–Vis diffuse reflectance spectroscopy and in situ Fourier Transform Infrared Spectroscopy (In situ DRIFTS) spectra. (BiO)2CO3 with different crystal structure and dominating facet were obtained and show a better photocatalytic performance of NO removal under visible light irradiation. Our research indicates that dominating facet is more related to the crystal structure, which affects the photocatalytic performance.

Small-molecule surface-modified bismuth-based semiconductors as a new class of visible-light-driven photocatalytic materials: Structure-dependent photocatalytic properties and photosensitization mechanism

Visible light photocatalysis driven via ligand-to-metal charge transfer (LMCT) can provide a new opportunity for solar energy utilization, yet investigations on non-TiO2 catalysts are rather limited and the mechanism of LMCT remains unclear. This study focused on the controllable synthesis, applications, and LMCT photosensitization mechanism of bismuth-based materials. BiOIO3, with tunable surface-exposed Bi(III), was first synthesized by a facile hydrothermal route and then applied to visible light photocatalytic decomposition of six dihydroxybenzoic acids (DHBAs) to optimize the conditions of surface complexation and photosensitization. After that, nine additional DHBA analogues and seven bismuth-based semiconductors with different crystal and band structures were used as alternative ligands and modified materials, respectively, to verify and support the hypothesis. It was found that organics with an ortho-dihydroxyphenyl substructure could chelate well with Bi(III) to form colored metal-organic complexes and caused the formation of surface oxygen vacancies (OVs) in the semiconductors, which resulted in the structural dependence and selective photocatalytic properties over the catalysts. In addition, the obtained materials could be used as either normal visible-light-driven photoelectric conversion materials or photocatalysts for environmental contaminants removal through producing highly reactive •OH, O2−, and 1O2 oxygen species. Theoretical calculations were performed to analyze the coordination, light absorption, molecular orbitals, and band structures of the complexes. With reference to the principles of semiconductor heterojunction, a novel visible-light-sensitization mechanism for small-molecule surface-modified bismuth-based semiconductors was proposed. The results develop the LMCT mechanism and significantly extend the applications of semiconductor photocatalytic materials.

Construction of CuO/CdS composite nanostructure for photodegradation of pollutants in sewage

The composite of semiconductor photocatalytic materials can effectively improve the solar energy utilization efficiency and quantum efficiency. Therefore, composite semiconductor materials have gradually become one of the most promising photocatalyst for solving water pollution problems. In this work, CuO nanowire arrays were prepared on Cu substrate by a thermal oxidation method, then CuO/CdS composite nanostructure was synthesized through an SILAR technique sequentially. The morphology, micro-area element composition, phase structure and optical properties of CuO/CdS nanostructure were characterized by field emission scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, ultraviolet–visible and photoluminescence spectroscopy respectively. Based on the test results, we systematically discussed the effects of several experimental conditions such as copper substrate, annealing temperature and reaction time on the properties and structure of CuO/CdS composite nanostructure. The resultant binary CuO/CdS composite nanostructure exhibited more excellent photocatalytic activity than pure CuO nanowire arrays both in the photodegradation of simulated contaminant methylene blue (MB) and practical pollutants of sewage.

An All-Organic Semiconductor C3 N4 /PDINH Heterostructure with Advanced Antibacterial Photocatalytic Therapy Activity.

Antibacterial photocatalytic therapy has been reported as a promising alternative water disinfection technology for combating antibiotic-resistant bacteria. Numerous inorganic nanosystems have been developed as antibiotic replacements for bacterial infection treatment, but these are limited due to the toxicity risk of heavy metal species. Organic semiconductor photocatalytic materials have attracted great attention due to their good biocompatibility, chemically tunable electronic structure, diverse structural flexibility, suitable band gap, low cost, and the abundance of the resources they require. An all-organic composite photocatalytic nanomaterial C3 N4 /perylene-3,4,9,10-tetracarboxylic diimide (PDINH) heterostructure is created through recrystallization of PDINH on the surface of C3 N4 in situ, resulting in enhanced photocatalytic efficiency due to the formation of a basal heterostructure. The absorption spectrum of this composite structure can be extended from ultraviolet to near-infrared light (750 nm), enhancing the photocatalytic effect to produce more reactive oxygen species, which have an excellent inactivation effect on both Gram-negative and positive bacteria, while demonstrating negligible toxicity to normal tissue cells. An efficient promotion of infectious wound regeneration in mice with Staphylococcus aureus infected dermal wounds is demonstrated. This all-organic heterostructure shows great promise for use in wound disinfection.

Novel Photocatalytic Nanocomposite Made of Polymeric Carbon Nitride and Metal Oxide Nanoparticles.

Semiconducting polymers are promising materials for photocatalysis, batteries, fuel applications, etc. One of the most useful photocatalysts is polymeric carbon nitride (PCN), which is usually produced during melamine condensation. In this work, a novel method of obtaining a PCN nanocomposite, in which PCN forms an amorphous layer coating on oxide nanoparticles, is presented. Microwave hydrothermal synthesis (MHS) was used to synthesize a homogeneous mixture of nanoparticles consisting of 80 wt.% AlOOH and 20 wt.% of ZrO2. The nanopowders were mechanically milled with melamine, and the mixture was annealed in the temperature range of 400–600 °C with rapid heating and cooling. The above procedure lowers PCN formation to 400 °C. The following nanocomposite properties were investigated: band gap, specific surface area, particle size, morphology, phase composition, chemical composition, and photocatalytic activity. The specific surface of the PCN nanocomposite was as high as 70 m2/g, and the optical band gap was 3 eV. High photocatalytic activity in phenol degradation was observed. The proposed simple method, as well as the low-cost preparation procedure, permits the exploitation of PCN as a polymer semiconductor photocatalytic material.

Efficient hydrogen generation of indium doped BaTiO3 decorated with CdSe quantum dots: Novel understanding of the effect of doping strategy

Doping has been widely utilized as an effective method of semiconductor modification to enhance photocatalytic efficiency. Most researches focus only on the effect of doping on decreasing band gap and inhibiting carriers recombination, however, the proximity of conduction band minimum (CBM) and valence band maximum (VBM) indicates the decrease of energy level and redox potential. Therefore, to further investigate the effect of doping on photocatalytic activity, the composite structure consisted of CdSe quantum dots (QDs) and indium doped BaTiO3 is synthesized by plain hydrothermal and chemical bath means. Under the condition of maintaining CdSe QDs optimal load ratio of 7.5 mol.%, doping 2.5% indium maximizes hydrogen production (0.437 mmol g–1 h–1) compared to undoped composite structure (0.258 mmol g–1 h–1), which originates from the increase of photo-induced electron reductive activity. The results suggest that we can use doping in reverse thinking to provide a new tactics for the design of semiconductor photocatalytic materials.

Antibacterial and photocatalytic properties of Cu2O/ZnO composite film synthesized by electrodeposition

The high antibacterial and photocatalytic activities of Cu2O/ZnO composite films were synthesized through the electrodeposition method. The crystalline phase and microstructure of the film samples were analyzed based on X-ray diffraction and scanning electron microscopy. The Cu2O/ZnO composite film-50 min has uniform and compact film structure with a large surface area. Compared with neat Cu2O film, the spectral response range of Cu2O/ZnO composite film was clearly enlarged to 265–560 nm, indicating that it had stronger spectral response ability in both UV and visible light. Among all the photocatalytic film samples, the Cu2O/ZnO composite film-50 min showed a better antibacterial activity against Escherichia coli (90.23 %) and Staphylococcus aureus (88.78 %) under fluorescent light. In addition, the Cu2O/ZnO composite film-50 min also exhibited the optimal photocatalytic property for the degradation of formaldehyde (80.33 %) under LED light irradiation. Moreover, the high photocatalytic and antibacterial stability in the cycle experiment indicate that Cu2O/ZnO composite film-50 min could be an excellent semiconductor photocatalytic material with high usability in practical applications.

Preparation and Photocatalysis of Schlumbergera bridgesii-Like CdS Modified One-Dimensional TiO2 Nanowires on Zeolite

In recent years, composite semiconductor photocatalytic materials have received significant attention as a novel type of materials and technical means. So in this work, CdS-modified TiO2 nanowires are fabricated on natural zeolite by simple sol-gel and hydrothermal synthesis method. This novel composite semiconductor photocatalytic material has almost solved the shortcomings of pure TiO2, such as easy cohesion, low utilization rate, and exceedingly weak photocatalytic activities under visible light. The degradation efficiency of methylene blue dye in water is near to 90% with CdS-modified TiO2 nanowires/zeolite composite materials after 60 min under visible light, which indicated its huge potential application in wastewater treatment.

Research on Preparation and Properties of Textile Materials Deposited with Nanostructured Titanium Oxide

In the 21st century, environmental pollution has become increasingly serious. Pollution control and management has been the major issue and must be resolved. In this paper, TiO2 as a representative oxide semiconductor photo catalytic material, which is an ideal environmental pollution cleaning product due to its unique properties. The low temperature magnetron sputter coating was employed to deposit Nanostructured TiO2 films on the surface of nonwovens and polymer fibers to functionalize the textile materials. The use of magnetron sputter coating not only overcame the problems of Nanoparticle aggregation as filling particles, but also shortened the production processes and eliminated the water pollution. The use of magnetron sputter coating, on the other hand, could cut the processing cost. This research explored the formation principle, preparation techniques, properties and reliability of the Nanostructured TiO2 deposited on the surface of textile substrates to meet the demands of the markets for functional textiles.