Comprehensive functionality analysis of spent coffee grounds activated using a microwave-assisted method

Abstract

Despite the immense number of research on the activated carbon (AC) preparation for wastewater treatment, fewer fractions have been devoted to the microwave-assisted activation route, which is unfortunate considering its advantageous features. In regards, this study explores the feasibility of a simple and rapid microwave-assisted activation method to generate AC from the spent coffee ground (SCG) under various microwave powers (100-450 W). The physicochemical properties of the generated ACs were studied by Fourier transform infrared spectroscopy, scanning electron microscopy, nitrogen adsorption-desorption, and X-ray diffraction analysis. As attained, lower microwave powers generated ACs with higher surface areas, pore volumes, and pore size as well as dominant OH and C=O spectral bands, which can correspond to higher adsorption sites for a more effective methylene blue (MB) removal process. In parallel, the adsorption tests demonstrated that the lowest microwave power sample (SCG-100) exhibited the highest MB adsorption at equilibrium (35 ± 1.75 mg g−1) in the optimum conditions of 25 mg L−1 MB solution, pH 8, 6 hour duration, and 0.025 g adsorbent. The kinetic and isotherm studies revealed the MB adsorption onto SCG-100 was defined by the pseudo-first-order (R2 =0.9462) and Langmuir isotherm (R2 = 0.9617) models respectively. Thermodynamically, the adsorption process occurred in an exothermic, and spontaneous manner. The water quality analysis data further found that the total organic compound, biological, and chemical oxygen demand were successfully decreased in a 6-hour period. Therefore, it can be concluded that the microwave activation method was capable of generating highly functional absorbent material for pollutant adsorption application.