Preparation and application of visible-light-responsive Ni-doped and SnO2-coupled TiO2 nanocomposite photocatalysts

Adsorption and Visible Photocatalytic Synergistic Removal of a Cationic Dye with the Composite Material BiVO4/MgAl-LDHs

Adsorption and photocatalysis are effective in removing organic pollutants from wastewater. This study is based on the memory effects of MgAl-layered double hydroxides (MgAl-LDHs) after high-temperature calcination. By introducing bismuth vanadate (BiVO4) during the reformation of the layered structure via contact with water, a composite material BiVO4/MgAl-LDHs with enhanced adsorption and visible light catalytic performance was synthesized. The effects of the calcination temperature, ratio, initial methylene blue (MB) concentration, and catalyst dosage on the adsorption and photocatalytic performance were investigated. The BiVO4/MgAl-LDHs showed better photocatalytic performance than the pure BiVO4 and MgAl-LDHs. Under the optimal conditions, the proportion of MB adsorbed in 20 min was 66.1%, and the percentage of MB degraded during 100 min of photolysis was 92.4%. The composite photocatalyst showed good chemical stability and cyclability, and the adsorption-degradation rate was 86% after four cycles. Analyses of the adsorption and photocatalytic mechanisms for the composite material showed that synergistic adsorption and visible light photocatalysis contributed to the excellent catalytic performance of the BiVO4/MgAl-LDHs. A highly adsorbent photocatalytic composite material exhibiting outstanding performance was prepared via a simple, cost-effective, and environmentally friendly method, providing reference information for the removal of organic pollutants from liquids.

Volatile organic compounds (VOCs) removal by photocatalysts: A review

Amplified anthropogenic release of volatile organic compounds (VOCs) gets worse air quality and human health. Photocatalytic degradation of VOCs is the practical strategy due to its low cost, simplicity, high efficiency, and environmental sustainability. Different types of photocatalyst activated by UV and visible lights are applied for VOC degradation. This review tries to investigate the state-of-art of recently published papers on this subject with a focus on the high-efficiency photocatalyst. The novel photocatalysts are introduced and enhancing photocatalytic activity strategies such as the hybrid of two/three photocatalyst, impurity doping, and heterojunctions with narrow bandgap semiconductors have been explained. The procedures of visible light activation of the photocatalysts are discussed with attention to current problems and future challenges. In addition, effective operational parameters in the photocatalytic degradation of VOCs have been reviewed with their advantages and drawbacks. A series of strategies are developed for the efficient utilization of visible light photocatalysts and improving new materials or design structures to degrade produced toxic intermediates/by-products during photocatalytic degradation of VOCs. This review shows that there are significant challenges in the applications of photocatalysts in the selective removal of VOCs. Several approaches should be combined to produce synergistic effects, which may lead to much higher photocatalytic performance than individual strategies. Another challenge is to develop efficient photocatalysts to meet real problems on an industrial scale.

Nano Metal-Containing Photocatalysts for the Removal of Volatile Organic Compounds: Doping, Performance, and Mechanisms

Volatile organic compounds (VOCs) in indoor air are considered a major threat to human health and environmental safety. The development of applicable technologies for the removal of VOCs is urgently needed. Nowadays, photocatalytic oxidation (PCO) based on metal-containing photocatalysts has been regarded as a promising method. However, unmodified photocatalysts are generally limited in applications because of the narrow light response range and high recombination rate of photo-generated carriers. As a result, nano metal-containing photocatalysts doped with elements or other materials have attracted much attention from researchers and has developed over the past few decades. In addition, different doping types cause different levels of catalyst performance, and the mechanism for performance improving is also different. However, there are few reviews focusing on this aspect, which is really important for catalyst design and application. This work aims to give a comprehensive overview of nano metal-containing photocatalysts with different doping types for the removal of VOCs in an indoor environment. First, the undoped photocatalysts and the basic mechanism of PCO is introduced. Then, the application of metal doping, non-metal doping, co-doping, and other material doping in synthetic metal-containing photocatalysts are discussed and compared, respectively, and the synthesis methods, removal efficiency, and mechanisms are further investigated. Finally, a development trend for using nano metal-containing photocatalysts for the removal of VOCs in the future is proposed. This work provides a meaningful reference for selecting effective strategies to develop novel photocatalysts for the removal of VOCs in the future.

A High-Performing Nanostructured Ir Doped-TiO2 for Efficient Photocatalytic Degradation of Gaseous Toluene

TiO2-based photocatalysts still have some limitations such as large bandgap and low surface area, leading to low efficiency in the photocatalytic degradation of VOCs and limiting it to use in sunlight. Here we report that the nanostructured Ir-doped TiO2 as an efficient photocatalyst generates an excellent risk-reduction material of gaseous toluene. We have succeeded in developing a nanostructured Ir-doped TiO2 and initially found that excellent efficient photocatalytic VOC decomposition can be achieved in our materials The nanostructured Ir-doped TiO2 was synthesized by a one pot, low temperature hydrothermal process with different ratios of Ir doped into the TiO2. It exhibited a high surface area, uniformly spherical morphology of 10–15 nm. Its activity for the photocatalytic degradation of gaseous toluene exhibited up to 97.5% under UV light. This enhancement could be explained by iridium doping which created a high concentration oxygen vacancy and changed the recombination rate of the photogenerated charge carriers. More generally, our study indicates a strategic way to develop the novel nanostructured material for numerous applications.

Investigation of the Sn4+-distribution and photocatalytic performance of Sn4+/TiO2 hollow fiber nanomaterials

Tin ion-doped TiO2 fibers were smartly prepared, and the distribution depth of Sn4+ influences the photocatalytic performance of TiO2.

Photocatalytic Technology for Palm Oil Mill Effluent (POME) Wastewater Treatment: Current Progress and Future Perspective

The palm oil industry produces liquid waste called POME (palm oil mill effluent). POME is stated as one of the wastes that are difficult to handle because of its large production and ineffective treatment. It will disturb the ecosystem with a high organic matter content if the waste is disposed directly into the environment. The authorities have established policies and regulations in the POME waste quality standard before being discharged into the environment. However, at this time, there are still many factories in Indonesia that have not been able to meet the standard of POME waste disposal with the existing treatment technology. Currently, the POME treatment system is still using a conventional system known as an open pond system. Although this process can reduce pollutants’ concentration, it will produce much sludge, requiring a large pond area and a long processing time. To overcome the inability of the conventional system to process POME is believed to be a challenge. Extensive effort is being invested in developing alternative technologies for the POME waste treatment to reduce POME waste safely. Several technologies have been studied, such as anaerobic processes, membrane technology, advanced oxidation processes (AOPs), membrane technology, adsorption, steam reforming, and coagulation. Among other things, an AOP, namely photocatalytic technology, has the potential to treat POME waste. This paper provides information on the feasibility of photocatalytic technology for treating POME waste. Although there are some challenges in this technology’s large-scale application, this paper proposes several strategies and directions to overcome these challenges.

New approach for the transformation of metallic waste into nanostructured Fe3O4 and SnO2-Fe3O4 heterostructure and their application in treatment of organic pollutant

Appropriate recycling of waste to reusable materials is much sought after in the scientific community to control the incessant rising pollution in environment due to insufficient management of waste materials. To address this issue, efforts were directed to obtain SnO₂-Fe₃O₄ nanocomposites from scrap tin plated steel and the use of these composites for the degradation of organic pollutant. We have demonstrated a novel, efficient and facile hydrometallurgy approach for the extraction of iron from waste tin plated steel containers found in plenty in the common waste generated in society. The extracted iron has further been utilized for the preparation of SnO₂:Fe₃O₄ nanocomposites with different compositions (SnO₂:Fe₃O₄ ratio of 93.2:6.8, 85:15, 58:42 and 40:60) using hydrothermal route. The photocatalytic activities of nanocomposite were determined spectroscopically using Rhodamine-B (RhB) as a model dye. Our results indicate that among all the composites with SnO₂ (85%):Fe₃O₄ (15%) exhibits the best photocatalytic efficiency under UV light whereas the composition of SnO₂ (93.2%):Fe₃O₄ (6.28%) is the most efficient in visible light. The above visible light efficiency was supported by density functional theory (DFT) studies which suggest a small amount of pure Fe is present at the Sn sites in the nanocomposite, leading to the reduction in the band gap of the nanocomposite and resulting in absorption in the visible range. Thus, in the present study, we have shown a process of conversion of waste to nanomaterials and its utilization for treatment of organic pollutants.

Enhanced photocatalytic activity in electrospun bismuth vanadate nanofibers with phase junction

BiVO4 nanofibers were successfully prepared by electrospinning and precisely controlled heat treatment. The obtained BiVO4 nanofibers showed an enhanced photocatalytic activity in the degradation of rhodamine-B under visible light irradiation. The as-prepared nanofibers were characterized by means of numerous techniques. The enhanced photocatalyst activity is attributed to the formation of a phase junction of tetragonal sheelite (s-t) and monoclinic sheelite (s-m) phases in the electrospun BiVO4 nanofibers. We have also investigated the band structure of BiVO4 using first principle calculation. The main photon transition mechanism of the photocatalyst should be from the O 2p to V 3d state of s-m/t BiVO4 nanofibers.

Synthesis, characterization and photocatalytic activity of magnetically separable γ-Fe2O3/N,Fe codoped TiO2 heterojunction for degradation of Reactive Blue 4 dye

Nanocrystalline undoped, N-doped and N,Fe codoped TiO₂ have been synthesized using a sol–gel method for the photocatalytic degradation of Reactive Blue 4 dye under visible light, with N,Fe codoped TiO₂ exhibiting the best activity.

Structure, enhancement and white luminescence of multifunctional Lu₆O₅F₈:20%Yb³⁺,1%Er³⁺(Tm³⁺) nanoparticles via further doping with Li⁺ under different excitation sources

A series of Lu6O5F8:20%Yb(3+),1%Er(3+)(Tm(3+)),x%Li(+) (0 ≤ x ≤ 12) nanoparticles with average size from 20 to 320 nm upon increasing Li(+) concentration were prepared by a coprecipitation method. The detailed crystal structure of Lu6O5F8 as a new matrix is firstly analysed via retrieved refinement of the powder X-ray diffraction (XRD). In addition, the corresponding Powder Diffraction File card information was also obtained through indexing the XRD pattern of the host. Upconversion under excitation at 980 nm, downconversion with Xe lamp as excitation source and cathodoluminescence properties of Lu6O5F8:20%Yb(3+),1%Er(3+)(Tm(3+)),x%Li(+) (0 ≤ x ≤ 12) nanoparticles were compared and studied. It is worthwhile pointing out that according to the effects of Li(+) on emission intensity ratio, white UC emission was achieved in the Lu6O5F8:6%Yb(3+),0.3%Er(3+),0.4%Tm(3+),5%Li(+) compared to Li(+) free sample with the same activator concentration. The reasons behind this behavior were presented and discussed. All in all, Li(+) ion would be a wonderful luminescence intensifier for lanthanide ions, and the multifunctional lanthanide ion-doped Lu6O5F8 nanoparticles have potential application in photoluminescence areas and field emission display devices.

Porous TiO2-Al2O3 Photocatalyst: The Effects of Calcination Time

Porous TiO2-Al2O3 composite materials were prepared through sol-gel method after calcination at 500 oC for different time. FT-IR spectra of porous TiO2-Al2O3 composite materials revealed that the samples are composed of Al2O3 and TiO2. The sample calcinated for 2.5 h had the maximum specific area of 128.9 m2•g-1. High pore volume and average pore size were possessed by the samples calcinated for 1 h and 3 h. While being calcinated at 500 oC, photocatalytic activities of the materials increased at first and then dropped down with the increasing calcination time. The sample calcinated for 3 h showed the maximum activity of 35%.

Processing-structure-property relationships of Bi2WO6 nanostructures as visible-light-driven photocatalyst

QDS modified Bi(2)WO(6) (BWO) nanostructures were processed by calcination at different temperatures. A strong correlation was found among the processing, structure and properties of the samples. With increasing calcination temperature from 200°C to 500°C, the crystallinity increased and the BWO QDS gradually disappeared from the nanostructures. Both surface area and band gap of the samples decreased. The light absorption of the samples became lower for the long-wavelength range, accompanied by a red shift of the absorption edge. The photocatalytic activity of the samples decreased after calcination at higher temperature. The competitive relations between crystallinity and surface area in affecting photocatalytic activity were discussed. The role of BWO QDS that played in enhancement of photocatalytic activity was also revealed by studying structure and property evolution of the calcined samples.

Photo degradation of methyl orange by attapulgite-SnO2-TiO2 nanocomposites

Photocatalytic removal of methyl orange under ultraviolet radiation has been studied using attapulgite (ATT) composites, which were synthesized by depositing SnO(2)-TiO(2) hybrid oxides on the surface of ATT to form a composite photocatalyst (denoted ATT-SnO(2)-TiO(2)) using an in situ sol-gel technique. Results showed that SnO(2)-TiO(2) nanocomposite particles with average size of about 10nm were loaded successfully on to the surface of ATT fibers and were widely dispersed. Correspondingly, the photocatalytic activity of ATT was improved significantly by loading SnO(2)-TiO(2). The photoactivity of the composite photocatalyst decreased in the sequence ATT-SnO(2)-TiO(2)>ATT-SnO(2)>ATT-TiO(2)>ATT. In order to achieve the best photocatalyst, the molar ratio of SnO(2) and TiO(2) in the ATT-SnO(2)-TiO(2) composites was adjusted to give a series with proportions r=n(Ti)/(n(Ti)+n(Sn))=0.0, 0.25, 0.33, 0.50, 0.67, 0.75, 0.80, 0.82, 0.86, 1.0. Results indicated that the proportion of SnO(2) and TiO(2) had a critical effect on the photocatalytic activity, which increased as the content of TiO(2) increased to r<or=0.82 and decreased when r>0.82. The highest degradation rate of methyl orange was 99% within 30 min obtained by using ATT-SnO(2)-TiO(2) with r=0.82. The repeated use of the composite photocatalyst was also confirmed.