InVO4/TiO2 composite for visible-light photocatalytic degradation of 2-chlorophenol in wastewater

Nano-architectural design of TiO2 for high performance photocatalytic degradation of organic pollutant: A review

In the past several decades, significant efforts have been paid toward photocatalytic degradation of organic pollutants in environmental research. During the past years, titanium dioxide nano-architectures (TiO₂ NAs) have been widely used in water purification applications with photocatalytic degradation processes under Uv/Vis light illumination. Photocatalysis process with nano-architectural design of TiO₂ is viewed as an efficient procedure for directly channeling solar energy into water treatment reactions. The considerable band-gap values and the subsequent short life time of photo-generated charge carriers are showed among the limitations of this approach. One of these effective efforts is the using of oxidation processes with advance semiconductor photocatalyst NAs for degradation the organic pollutants under UV/Vis irradiation. Among them, nano-architectural design of TiO₂ photocatalyst (such as Janus, yolk-shell (Y@S), hollow microspheres (HMSs) and nano-belt) is an effective way to improve oxidation processes for increasing photocatalytic activity in water treatment applications. In the light of the above issues, this study tends to provide a critical overview of the used strategies for preparing TiO₂ photocatalysts with desirable physicochemical properties like enhanced absorption of light, low density, high surface area, photo-stability, and charge-carrier behavior. Among the various nanoarchitectural design of TiO₂, the Y@S and HMSs have created a great appeal given their considerable large surface area, low density, homogeneous catalytic environment, favorable light harvesting properties, and enhanced molecular diffusion kinetics of the particles. In this review was summarized the developments that have been made for nano-architectural design of TiO2 photocatalyst. Additional focus is placed on the realization of interfacial charge and the possibility of achieving charge carriers separation for these NAs as electron migration is the extremely important factor for increasing the photocatalytic activity.

Enhanced immobilization of mercury (II) from desulphurization wastewater by EDTA functionalized graphene oxide nanoparticles

Graphene oxide (GO) is a new promising nanometer material in a superconductor and wastewater heavy metal ions removal for its functionalized groups. Ethylenediaminetetraacetic acid functionalized graphene oxide complexes (EDTA-GO) was produced by a realizable silanization chemical reaction. Characteristics of Hg(II) removal in desulphurization wastewater was also under investigation. The chemical composition and microstructures of the EDTA-GO adsorbents were characterized by X-ray photoelectron spectroscopy (XPS), Transmission electron microscope (TEM), Scanning Electron Microscopy (SEM) analyses. To investigate the performance of EDTA-GO adsorbents on adsorption of Hg(II) in wastewater of wet flue gas desulphurization (WFGD), experiments were performed to optimize the main influence factors such as reaction temperatures (35-70°C), pH values(2-13), contact time (0-120 min), initial Hg(II) concentrations(800 ug/L) and adsorbent doses (20-50 mg/L). The maximum uptake removal efficiency (97.14%) was achieved under the optimal conditions at the pH of 7, the temperature of 70°C, the Hg(II) concentration of 1200 μg/L and the EDTA-GO dose of 40 mg/L. The kinetic data fitting results were well consistent with the pseudo-second-order model (R²= 0.99997) and a spontaneous and endothermic adsorption reaction was elaborated by thermodynamics studies (ΔG < 0, ΔH > 0, ΔS > 0). The experiments of recycled adsorbents by HCl generation were carried out to obtain the performance of the reused EDTA-GO adsorbent, the fourth regenerative adsorption efficiency still maintained 80.4%, which indicated that excellent potential application in desulphurization wastewater treatment.

Butterfly cluster like lamellar BiOBr/TiO2 nanocomposite for enhanced sunlight photocatalytic mineralization of aqueous ciprofloxacin

The present study for the first time reports facile in-situ room temperature synthesis of butterfly cluster like lamellar BiOBr deposited over TiO₂ nanoparticles for photocatalytic breakdown of ciprofloxacin (CIP). The butterfly cluster arrangement of BiOBr resulted in an increase in surface area from 124.6 to 160.797 m²·g^-1 and subsequently increased incident light absorption by the composite photocatalyst. The XRD indicated the existence of TiO₂ as spherical ≈10-15 nm diameter particles with [101] preferential growth planes of anatase phase while the lamellar BiOBr showing growth along [110] and [102] preferential planes that were also confirmed by the HR-TEM images. DRS data implicated 2.76 eV as the energy band gap of the synthesized nanocomposite while PL spectroscopic analysis predicted it to be 2.81 eV. XPS measurements examined the chemical oxidation states of the constituents among the nanocomposite samples. The lameller structure of BiOBr in 15%BiOBr/TiO₂ acts as a manifold promoting both visible light (λ > 420 nm) and direct sunlight catalytic degradation of 25 mg·L^-1 aqueous CIP up to 92.5% and 100%, respectively within 150 min. The rate constant values suggested that the visible light photocatalysis of CIP with 15%BiOBr/TiO₂ was 5.2 and 9.4 times faster compared to pristine TiO₂ and BiOBr, respectively. The free radical scavenging study demonstrated that although photogenerated superoxide ions and holes contribute to the overall photocatalytic activity, yet, hydroxyl radicals predominantly control the CIP oxidation. The synthesized nanocomposite was re-used up to five cycles and retained 82.98% efficiency even after 5th use cycle showing a decline of only 12%. The catalyst stability and easy recovery adds to its reusability and value of the photocatalytic process.

Photodegradation performance and mechanism of 4-nonylphenol by WO3/TiO2 and TiO2 nanotube array photoelectrodes

TiO₂ Nanotube arrays (TNA) and WO₃-coated TNA photoelectrodes were fabricated using an in situ anodization and pulse electrochemical deposition technology. The performance of the TNA photoelectrodes in the photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of 4-nonylphenol (4-NP) was investigated. The effects of the initial pH and the anions on the degradation rates and reaction mechanism of 4-NP were studied by the photoluminescence (PL) spectra and electrochemical impedance spectra (EIS). The degradation of 4-NP was fitted to a first-order reaction, and the apparent kinetic constants were 1.9 × 10^-2 min^-1 for TNA photoelectrodes and 2.4 × 10^-2 min^-1 for WO₃/TNA photoelectrodes. When a bias potential of 1.0 V was applied, the values for TNA and WO₃/TNA photoelectrodes increased to 2.5 × 10^-2 and 3.0 × 10^-2 min^-1, respectively. The degradation of 4-NP was controlled by a charge-transfer process one. WO₃-decorated TNA photoelectrodes could increase the adsorption of 4-NP and promote its degradation. For the TNA and WO₃/TNAs photoelectrodes, acid and alkaline solutions could facilitate the formation of hydroxyl radicals, whereas the removal of 4-NP was inhibited. The presence of [Formula: see text] , Cl^-, [Formula: see text] and [Formula: see text] has a negative effect on the formation of •OH, so did the removal of 4-NP. For the TNA photoelectrodes, the inhibition effect of [Formula: see text] on the formation of hydroxyl radicals and the removal of 4-NP was the most serious compared with that of [Formula: see text], Cl^- and [Formula: see text] , while for the WO₃/TNA photoelectrodes the inhibition effect of [Formula: see text] on the removal of 4-NP was maximum.

Synthesis of akageneite (beta-FeOOH)/reduced graphene oxide nanocomposites for oxidative decomposition of 2-chlorophenol by Fenton-like reaction

In this work, the composite of reduced graphene oxide and akageneite (Ak/rGO) was synthesised by co-precipitating and reduction processes. The morphological and structural features of the synthesized composites (Ak/rGO) were characterized by XRD, SEM, BET, FTIR, Zeta potential and XPS. The results revealed that (1) beta-FeOOH was successfully loaded on the reduced graphene oxide (rGO); (2) the presence of strong interfacial interactions (Fe-O-C bonds) between rGO and beta-FeOOH was observed; (3) the reduction of graphene oxide may be inhabited in the formation process of beta-FeOOH, producing rGO sheets rather than rGO sphere. In the heterogeneous Fenton-like reaction, the degradation rate constants of 2-chlorophenol (2-CP) increased 2-5 times after the addition of rGO probably due to the Fe-O-C bond. The increase of the content of rGO could contribute to the removal of 2-CP, due to the synergy of catalysis and 2-CP adsorption towards Ak/rGO. In this study, the Ak/rGO composite has exhibited great potential and significant prospects for environmental application.

Rapid photo-degradation of 2-chlorophenol under visible light irradiation using cobalt oxide-loaded TiO2/reduced graphene oxide nanocomposite from aqueous media

The photocatalytic removal of 2-chlorophenol (2-CP) from water environment was investigated by TiO2-RGO-CoO. Cobalt oxide-loaded TiO2 (TiO2-CoO) supported with reduced graphene oxide (RGO) was synthesized using a sol-gel method and then annealed at 500 °C for 5 min. The material characteristics were analyzed by UV-Vis analysis, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. Incorporation of cobalt oxide and RGO into the TiO2 system (TiO2-RGO-CoO) lowered the band gap energy to 2.83 eV, which greatly enhanced the visible light absorption. The TiO2-RGO-CoO photocatalyst showed complete removal of 20 mg/L 2-CP within 8 h with the addition of 0.01% H2O2 under 100 W visible light irradiation. The photo-degradation efficiency of 2-CP (10 mg/L) was 35.2, 48.9, 58.9 and 98.2% for TiO2, TiO2-RGO, TiO2-CoO and TiO2-RGO-CoO, respectively, in the presence of visible light irradiation at solution pH of 6.0. The TiO2-RGO-CoO photocatalyst retained its high removal efficiency even after five photocatalytic cycles.