Photocatalytic degradation of pollutants in petroleum refinery wastewater by TiO2- and ZnO-based photocatalysts: Recent development

Titanium dioxide (TiO2) nanomaterials have garnered extensive scientific interest since 1972 and have been widely used in many areas, such as sustainable energy generation and the removal of environmental pollutants. Although TiO2 possesses the desired performance in utilizing ultraviolet light, its overall solar activity is still very limited because of a wide bandgap (3.0–3.2 eV) that cannot make use of visible light or light of longer wavelength. This phenomenon is a deficiency for TiO2 with respect to its potential application in visible light photocatalysis and photoelectrochemical devices, as well as photovoltaics and sensors. The high overpotential, sluggish migration, and rapid recombination of photogenerated electron/hole pairs are crucial factors that restrict further application of TiO2. Recently, a broad range of research efforts has been devoted to enhancing the optical and electrical properties of TiO2, resulting in improved photocatalytic activity. This review mainly outlines state-of-the-art modification strategies in optimizing the photocatalytic performance of TiO2, including the introduction of intrinsic defects and foreign species into the TiO2 lattice, morphology and crystal facet control, and the development of unique mesocrystal structures. The band structures, electronic properties, and chemical features of the modified TiO2 nanomaterials are clarified in detail along with details regarding their photocatalytic performance and various applications.

Titanium Dioxide: From Engineering to Applications

Photoelectrocatalysis (PEC) of sulfamethoxazole (SMZ) was investigated using TiO 2 /Ti (UV-A) photoanode. Complete photoelectrocatalytic degradation of SMZ was achieved after 70 min at 0.5 V, while SMZ resisted to photolysis and electrolysis. Langmuir-Hinshelwood analysis yielded an adsorption constant ( K ) of 0.519 L/mg for the studied PEC-TiO 2 system, with K being 3–4 times of those from photocatalysis. PEC degradation of SMZ accelerated with increasing anodic potential (0–0.5 V), declining pH (from 10.1 to 2.7), and increasing NaCl concentration (1–100 mM). These trends were consistent with the understanding that higher potential gradient reduces recombination of holes and electrons, lower pH favors photoadsorption through modulation of SMZ speciation and TiO 2 surface charge, and higher Cl − level encourages formation of chlorine radicals. Molar ratios of HO and chlorine radicals showed that the effects of pH and Cl − levels were coupled, with the level of PEC activity linked to the relative dominance of [Cl 2 − ] over [HO ]. In the presence of radical scavengers, SMZ photoelectrocatalysis was lowered by 30% at merely 10 mg/L of humic acid, and was reduced to and Cl 2 − /active chlorine species were the main oxidants in a Cl − -present environment. A 3-times above-average photocurrent was observed in 10% methanol, whose unusual photocurrent increase was attributed to sequential current doubling – additional electron flow due to reactive adsorbate-hole interaction – through a series of proposed reactions: conversion of h V B + -bound methanol through formaldehyde and formic acid to CO 2 . Implications of the findings with respect to practical application of PEC are presented.

Photoelectrocatalytic degradation of the antibiotic sulfamethoxazole using TiO2/Ti photoanode

In recent years, the application of heterogeneous photocatalytic water purification process has gained wide attention due to its effectiveness in degrading and mineralizing the recalcitrant organic compounds as well as the possibility of utilizing the solar UV and visible light spectrum. This paper aims to review and summarize the recently published works on the titanium dioxide (TiO2) photocatalytic oxidation of pesticides and phenolic compounds, predominant in storm and waste water effluents. The effect of various operating parameters on the photocatalytic degradation of pesticides and phenols are discussed. Results reported here suggested that the photocatalytic degradation of organic compounds depends on the type of photocatalyst and composition, light intensity, initial substrate concentration, amount of catalyst, pH of the reaction medium, ionic components in water, solvent types, oxidizing agents/electron acceptors, catalyst application mode, and calcinations temperature in water environment. A substantial amount of research has focused on the enhancement of TiO2 photocatalysis by modification with metal, non-metal and ion doping. Recent developments in TiO2 photocatalysis for the degradation of various pesticides and phenols are also highlighted in this review. It is evident from the literature survey that photocatalysis has shown good potential for the removal of various organic pollutants. However, still there is a need to find out the practical utility of this technique on commercial scale.

Influence of parameters on the heterogeneous photocatalytic degradation of pesticides and phenolic contaminants in wastewater : a short review

Microstructure characterization of hydrothermally synthesized PANI/V2O5·nH2O heterojunction photocatalyst for visible light induced photodegradation of organic pollutants and non-absorbing colorless molecules.

Kyungduk Kim

Papers

Photocatalytic degradation of phenol in water on as-prepared and surface modified TiO2 nanoparticles