Fabrication of Ag-decorated BiOBr-mBiVO4 dual heterojunction composite with enhanced visible light photocatalytic performance for degradation of malachite green

Enhanced photoelectrocatalytic degradation of diclofenac sodium using a system of Ag-BiVO4/BiOI anode and Ag-BiOI cathode

We report the photoelectrocatalysis of diclofenac sodium using a reactor consisting of Ag-BiVO4/BiOI anode and Ag-BiOI cathode. The electrodes were prepared through electrodeposition on FTO glass and modified with Ag nanoparticles through photodeposition. The structural and morphological studies were carried out using XRD, SEM, and EDS which confirmed the successful preparation of the materials. The optical properties as observed with UV-DRS revealed that the electrodes were visible light active and incorporation of metallic Ag particles on the surface increased the absorption in the visible light region. Presence of p-n heterojunction in the anode led to decrease in the spontaneous recombination of photoexcited electron-hole pairs as seen in the photocurrent response. The results from photoelectrocatalytic degradation experiments revealed that replacing platinum sheet with Ag-BiOI as counter electrode resulted in higher (92%) and faster removal of diclofenac sodium as evident in the values of apparent rate constants. The reaction mechanism further revealed that efficiently separated photogenerated holes played a major role in the degradation of the pharmaceutical. The prepared electrodes showed good stability and impressive reusability. The reports from this study revealed that the dual photoelectrodes system has a great potential in treating pharmaceutical polluted wastewater using visible light irradiation.

A high-efficiency mediator-free Z-scheme Bi2MoO6/AgI heterojunction with enhanced photocatalytic performance

A high-efficiency Z-scheme Bi₂MoO₆/AgI heterojunction was designed and fabricated via in situ growth of AgI on Bi₂MoO₆. Its photocatalytic activity was investigated with the degradation of malachite green (MG). After 40 min of visible light irradiation, near complete degradation of MG (20 mg/L) occurred when BA11 (Bi₂MoO₆:AgI = 1:1, 2.0 g/L) was present, while only 29.0% and 49.7% of the MG could be degraded in the presence of Bi₂MoO₆ and AgI, respectively. The excellent photocatalytic activity of BA11 results from strong visible light absorption and the low recombination efficiency of photogenerated electron-hole pairs induced by the formation of heterojunction. Density function theory (DFT) calculations revealed that the formation of built-in electric field at the interface between Bi₂MoO₆ and AgI facilitates the effective separation and transfer of photogenerated charge carriers. Results of reuse experiments indicated that the heterostructured photocatalyst has excellent stability. Radical scavenging experiments and electron spin resonance spectra showed that superoxide radicals (O₂^-) and hydroxyl radicals (OH) were the major reactive oxygen species in the photocatalytic system. The photocatalytic degradation pathway of MG was proposed based on the organic degradation intermediates detected. These findings demonstrate that the mediator-free Z-scheme Bi₂MoO₆/AgI heterojunction could serve as a promising photocatalyst in photocatalytic treatment of organic pollutants.

Effect of carbon nanotubes loading on the photocatalytic activity of BiSI/BiOI as a novel photocatalyst

In this paper, a simple hydrothermal method is employed to synthesize BiSI/BiOI/CNT nanocomposite with enhanced photocatalytic activity. The properties of the prepared samples were studied using nitrogen adsorption-desorption isotherm, photoluminescence, X-ray diffraction analysis (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive spectrometry (EDS), UV-vis diffuse reflectance spectroscopy (DRS), and electrochemical impedance spectroscopy (EIS). The loading amount of CNT had a significant influence on the photoactivity of the BiSI/BiOI/CNT composite. In this study, several BiSI/BiOI/CNT nanocomposite samples with various mass ratios of CNT were made-up for further investigation to scrutinize the influence of CNT content on the photocatalytic activity of the nanocomposite. Photocatalysis measurements revealed that 2% Wt of CNT possesses the highest photocatalytic activity in the visible light irradiation with 93.1% photodegradation of malachite green (MG) as a test dye. The enhanced photocatalytic performance can be due to the large surface area, excellent conductivity performance, and high absorption ability in the visible light region. The synergistic effect of the factors mentioned above makes BiSI/BiOI/CNT nanocomposite a high-performance photocatalyst under visible light irradiation. An appropriate reaction mechanism of dye photodegradation has suggested according to the result of active species trapping experiments.

Synthesis of γ-alumina (Al2O3) nanoparticles and their potential for use as an adsorbent in the removal of methylene blue dye from industrial wastewater

Non-toxic nanomaterials have gained significant importance recently in the treatment of industrial wastewater that sometimes contains organic dyes such as methylene blue. We report here an easy approach for the synthesis of γ-alumina (Al₂O₃) nanoparticles via a method that incorporates the use of formamide and the non-ionic surfactant Tween-80. Together, formamide and Tween-80 serve as an effective precipitating agent and a convenient synthetic template, respectively, in directing the growth of the alumina nanoparticles. The morphology and structure of the nanoparticles were investigated by FT-IR, XRD, TGA, SEM, EDX, elemental mapping and TEM methods. The sizes of the nanoparticles are in the 30-50 nm range. The maximum pore size is 4.13 nm and the surface area is 112.9 m² g^-1 as determined by the Brunauer-Emmett-Teller (BET) method. The nanomaterials are excellent adsorbents for the cationic methylene blue dye from aqueous solution. The effects of pH, time, temperature and concentration on the adsorption have been examined and the adsorption capacity increased from 490 to 2210 mg g^-1 as the initial concentration was increased from 50 to 400 mg L^-1 under the following conditions: pH 9, 10 min reaction time, and 60 °C. The adsorption mechanism is considered to encompass electrostatic interactions in water between the Al₂O₃ nanoparticles and the cationic methylene blue dye. These readily made nanoparticles may well prove useful in both wastewater treatment and industrial catalysis.

Low temperature synthesis of BiFeO3 nanoparticles with enhanced magnetization and promising photocatalytic performance in dye degradation and hydrogen evolution

In this investigation, we have synthesized BiFeO3 nanoparticles by varying hydrothermal reaction temperatures from 200 °C to 120 °C to assess their visible-light driven photocatalytic activity along with their applicability for hydrogen production via water splitting. The rhombohedral perovskite structure of BiFeO3 is formed for hydrothermal reaction temperature up to 160 °C. However, for a further decrement of hydrothermal reaction temperature a mixed sillenite phase is observed. The XRD Rietveld analysis, XPS analysis and FESEM imaging ensure the formation of single-phase and well crystalline nanoparticles at 160 °C reaction temperature with 20 nm of average size. The nanoparticles fabricated at this particular reaction temperature also exhibit improved magnetization, reduced leakage current density and excellent ferroelectric behavior. These nanoparticles demonstrate considerably high absorbance in the visible range with a low band gap (2.1 eV). The experimentally observed band gap is in excellent agreement with the calculated band gap using first-principles calculations. The favorable photocatalytic performance of these nanoparticles has been able to generate more than two times of solar hydrogen compared to that produced by bulk BiFeO3 as well as commercially available Degussa P25 titania. Notably, the experimentally observed band gap is almost equal for both bulk material and nanoparticles prepared at different reaction temperatures. Therefore, in solar energy applications, the superiority of BiFeO3 nanoparticles prepared at 160 °C reaction temperature may be attributed not only to their band gap but also to other factors, such as reduced particle size, excellent morphology, good crystallinity, large surface to volume ratio, ferroelectricity and so on.