Preparation and characterization of N-doped ZnO and N-doped TiO2 beads for photocatalytic degradation of phenol and ammonia

Abstract

N-doped ZnO beads (NZB) and N-doped TiO2 beads (NTB) were synthesized via a modified sol–gel technique utilizing chitosan (CS)/polyvinyl alcohol (PVA) hydrogel beads as basic support for photocatalyst. Urea was used as a source of nitrogen in the preparation of N-doped ZnO beads, while ammonium acetate, CH3COONH4, was used as a nitrogen source in the production of N-doped TiO2 beads. The characteristics of synthesized beads were identified by scanning electron microscope (SEM), X-ray photoelectron spectroscopy analysis (XPS), X-ray diffraction (XRD), N2 adsorption–desorption isotherms, BET surface area, Fourier transform infrared (FT-IR) measurements, and diffuse reflectance spectroscopy (DRS) studies. The use of the nitrogen doping method for photocatalyst was performed to adjust the bandgap and electrical properties of ZnO and TiO2 by establishing acceptor defects. NZB and NTB with the intrinsic donor defect of oxygen vacancy and the nitrogen-to-oxygen acceptor defect could be activated by a less-energy UV consumption for efficient pollutant degradation. The results indicated that the as-synthesized NZB achieved much higher degradation activity than NTB, commercial ZnO, and TiO2 in the decomposition of a binary mixture composed of ammonia and phenol under UV light irradiation.

Behavior of N-Doped TiO2 and N-Doped ZnO in Photocatalytic Azo Dye Degradation under UV and Visible Light Irradiation: A Preliminary Investigation

“…Instead, the electron transfer from the donor sites (V O ) to the acceptor sites (N) determines a shift of the Fermi level toward the conduction band of ZnO, decreasing the mobility of the holes. Although the available literature [56,57] contains some reports of an enhancement in photocatalytic activity, the results in terms of EBT discoloration (Figure 6b) show that doping with nitrogen is not an efficient way to enhance the chemical reactivity of ZnO in the UV region [58]. Moreover, the achieved results could be also attributed to the concentration of N in the ZnO lattice, which could affect the photocatalytic activity.…”

A Review of Synthesis Methods, Modifications, and Mechanisms of ZnO/TiO2-Based Photocatalysts for Photodegradation of Contaminants

“…Some elements like N, C, S, B, P, I, and F as dopants are used to narrow the band gap energy and extend the recombination time of electrons and holes to improve the photocatalytic efficiency . Nitrogen, due to its similarity with oxygen in terms of ionic radius and 2p energy level, is commonly used as a modifying agent and replaces with oxygen in the photocatalytic lattice. − On the other hand, doping with carbon materials is an effective approach to change the optical properties of the photocatalysts and improve photocatalytic activity due to the electron transfer potential, light absorption, and physicochemical durability of carbons as dopants . Sulfur, the same as oxygen, is a VIA group element that has comparable physicochemical properties, but the ionic radius and electronegativity values of sulfur are different.…”

TiO2−x prepared by radio-frequency thermal plasma: optical switching of hydrophilicity and hydrophobicity used in the efficient recovery of photocatalysts

“…Most recent studies have mainly focused on increasing the quantum efficiency, enhancing the visible light utilization efficiency and restraining the high recombination between the photogenerated electron-hole pairs of TiO 2 (ref. 1) by modifying the TiO 2 catalyst through various methods, such as compositing with narrow-band gap semiconductors, 2 doping with metal ions 3,4 or non-metal ions, [5][6][7] mixing with carbon materials, 8 or introducing oxygen vacancies (V O ) 9 to obtain better catalytic efficiency.…”