Vanadium-doped CuO: Insight into structural, optical, electrical, terahertz, and full-spectrum photocatalytic properties

Abstract

Aiming to widen the band gap, minimize the charge-carrier recombination, and enhance the transport properties, we reported the first synthesis of high purity vanadium-doped CuO as a promising photocatalyst nanopowder for water purification. Pure CuO and Cu1-xVxO (where x = 0.00, 0.01, 0.03, 0.05, and 0.07 mol) were synthesized by a facile sol-gel technique. The structural investigation performed by both X-ray and selected area electron diffraction patterns evidenced the formation of highly pure monoclinic CuO. The vanadium inclusion caused a noticeable red shift in Bragg's positions. The grain size was estimated by both Debye-Scherrer and Halder-Wagner methods and ranged from 21 to 28 nm. All the vibrational absorption bands disclosed by FTIR measurement are affiliated with monoclinic CuO exhibiting a small shift for V-doped nanopowders. The stoichiometry of the constituent elements (Cu, O, and V) was assured by energy dispersive X-ray analysis (EDX). The presence of agglomeration is the main feature in field emission scanning electron microscope images revealing the nanostructure property of CuO. The band gap energy of Cu0.93V0.07O determined from diffuse reflectance is 1.44 eV which meets exactly the peak of the solar spectrum rendering it a promisingly photocatalytic material. The rise of absorption in the terahertz range as measured by THz time-domain spectroscopy (THz-TDS) established the increase of density of states owing to the inclusion of vanadium. The incorporation of 0.07 mol of V considerably increases the free sunlight photocatalytic activity of CuO for high concentration Congo red pollutant (20 ppm) from 30 to 76% at the same time of 100 min (over 1.53 times as pure CuO)