facile hydrothermal synthesis of fe3+ doped zinc oxide with improved photocatalytic performance under visible light radiation

Nowadays, water pollution is becoming more and more dangerous, which brings overwhelming issues to our society [1]. water pollution resulting from textile dyeing and other industrial process has been one of the severe health hazards for people. to deal with this problem and cleaning wastewater from toxic dye substrates, many research groups have focused on the development of some physical, chemical and biological methods [2]. in the last decades, heterogeneous photocatalysis for wastewater treatment applications has been developed. photocatalysis is an advanced technology, has been applied for the photodegradation of various organic pollutants owing to its high efficiency, simple equipment, ease of operation, low energy consumption, and high oxidation capacity [3, 4]. zinc oxide is a reasonable choice as a photocatalyst in which its mechanism of photocatalysis has been proven to be similar to that of tio2. zno also acquires many advantages, such as low price, many active sites with high surface reactivity, high absorption efficacy of light radiations, and environmental-safety [5]. however, a significant problem with zno photocatalyst is that it is active only under uv irradiation owing to its high band-gap. since solar light is composed of only 5–7% of uv light, therefore, low utilization of solar energy by zno photocatalysts greatly restricts its large-scale application. additionally, the recombination of photogenerated e−/h+ pairs in zno is very high owing to low quantum efficiency which severely reduces photocatalytic activity [3]. recently, transition metal ions such as co2+, ni2+, and fe3+ have been used as dopants of zno to improve its optical properties. doping with fe3+ not only enhances electron-hole pair separation by decrease the band-gap to make advantages of shifting the absorption to the visible light spectrumbut also decreases the size [6]. so, our current research has been directed toward developing zno doped with a concentration of fe3+ to improve its photocatalytic activity in the visible light region. pure and fe3+ doped zinc oxide nanoparticles (zno and fezno nps, respectively) were prepared using the hydrothermal method without the use of capping agent or surfactants and they were then characterized using x-ray diffraction (xrd), field-emission scanning electron microscopy (fesem), fourier-transform infrared spectroscopy (ftir) and diffuse reflectance spectrophotometry (uv-drs). the result of the analysis indicates the hexagonal wurtzite structure of these nanoparticles and fep 3+ p ions were well incorporated into the zno crystal lattice. the spectral absorption shifts to the visible light region and the band-gap decreased from 3.1ev to 2.86ev for the pure and fe-doped zno, respectively. the photocatalytic activity of the zno and fezno samples was evaluated by the degradation of methylene blue in aqueous solution under both uv and visible light radiations. the results show that fezno by 98.4% of dye degradation possesses higher photocatalytic activity than zno by that of 5.5% after 3 hours under visible light irradiation.