Visible-light-induced degradation of rhodamine B by nanosized Ag₂S-ZnS loaded on cellulose

In the present work, new visible-light-active nanosized Ag₂S-ZnS loaded on cellulose (AZCE) was synthesized by a precipitation method. The AZCE composite was systematically characterized using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area, and UV-visible diffuse reflectance spectroscopy (UV-DRS). The activities of the photocatalysts were evaluated for rhodamine B dye (RhB) degradation under simulated sunlight and the amounts of the dye samples were analysed using a UV-vis spectrophotometer at λ_max 554 nm. The effects of the reaction conditions such as pH, catalyst, hydrogen peroxide and dye concentration on the photodegradation rate have been investigated. The degradation profile reveals that 30 ppm of the dye could be effectively oxidized using 30 mg of the AZCE dose in the pH range 4-12 within 90 min. The oxidation of the RhB dye follows first-order kinetics and the rate constant was calculated to be 6.4 × 10^-3 min^-1. Various organic intermediates were identified during degradation using high performance liquid chromatography (HPLC), total organic content (TOC) and electron-spray ionization-mass spectrometry (ESI-MS). In order to determine the effectiveness of AZCE photocatalytic activity, other catalysts such as Ag₂S loaded on cellulose (AZE) and ZnS loaded on cellulose (ZCE) were used as photocatalysts. The results show that photocatalytic activity follows the order AZCE > ACE > ZCE and this is due to the fact that a cellulose network is used as a catalyst carrier. The alkali pre-treated cellulose provides an activated surface hydroxyl groups to enhance the deposition efficiencies of Ag₂S and ZnS and thereby a large amount of visible light can be absorbed and the photocatalytic activity is increased.