Porous zinc-discs as nanocatalysts for methylene blue dye treatment in water: sensing, adsorption and photocatalytic degradation

Abstract

This paper reports a zinc derived (ZD) porous nanosystem that has been used for selective sensing, adsorption, and photocatalytic degradation of the known hazardous dye, Methylene blue (MB). Using zinc nitrate and 2-aminoterphthalic acid as precursors, the synthesis has been optimized to yield disc-shaped nanoparticles. This luminescent ZD nanoparticles exhibit absorption and emission wavelengths of 328 nm and 427 nm, respectively at an excitation wavelength of 330 nm. In the presence of MB, there is a sharp decrease in the photoluminescence emission intensity of ZD nanoparticles. The detection limit, quenching constant and the binding constant of ZD nanoparticles with MB are found to be 0.31 × 10⁻⁹ M, 3.30 × 10⁶ M⁻¹ and 2.27 × 10⁶ M⁻¹ respectively. The impact of contact time, initial MB concentration, and pH on the adsorption process were investigated. The equilibrium data fit well with the Langmuir adsorption isotherm model (R² = 0.989) and superlatively fitted to the pseudo-second-order rate model (rate constant: 0.00011 g mg⁻¹ min⁻¹; adsorption capacity (q_{e, calc.}): 386.1 mg g⁻¹; R²: 0.990). Further, the MB dye degradation was performed under ultra-violet irradiation and ∼95% MB degradation was achieved within 70 min. The experimental data are well fitted to the pseudo-first order kinetics (R²: 0.99; rate constant: 0.015 min⁻¹). These disc shaped ZD nanoparticles can not only facilitate the detection, but also the adsorption and photocatalytic degradation of MB, which can be further processed for environmental remediation applications.