Polyethyleneimine modified acid treated spent tea as adsorbent for aspirin removal

Abstract

Adsorption is a prominent process for the treatment of pharmaceutical compounds in wastewater which uses activated carbon (AC) as the adsorbent material. Unfortunately, due to high preparation cost in terms of chemical and energy usage, and poor tendency to be regenerated, the usage of AC at high scale is limited. Hence, there is a need to shift towards new substitutes that are both inexpensive and highly efficient, such as agricultural waste materials. To overcome the drawbacks of the AC, this study focuses on the synthesis of a new modified eco-friendly adsorbent using spent tea (discarded Camellia sinensis leaves). Other than safe and simple preparation method, it is also of low energy consumption since all the synthesis steps were done at low temperature and free of harmful materials and chemicals. Its application in the adsorption of aspirin from aqueous solution were conducted by batch adsorption technique. In this study, spent tea was modified with polyethyleneimine (PEI) via a crosslinking method with the usage of glutaraldehyde (GTA) as the crosslinker for the removal of aspirin. The spent tea initially underwent acid pre-treatment with the usage of phosphoric acid for washing and boosting the functional group purpose and afterwards called acid treated spent tea (TA). The best conditions to prepare PEI modified acid treated spent tea (TA-PEI) were 1 hour of acid pre-treatment, TA: PEI ratio of 1:2, and GTA concentration of 0.5%v/v. Afterwards, the TA-PEI was characterized using the Fourier transform infrared spectroscopy, Brunauer Emmett Teller area, CHNS Elemental analysis, scanning electron microscope analysis, and point of zero charge (pHpzc). A batch experiment of adsorption studies was conducted and the results revealed a remarkable outcome with the adsorption capacity up to 88.9 mg/g under the following conditions: 30 minutes of contact time, pH 3, temperature of 30 °C, initial concentration of 200 mg/L and adsorbent dosage of 0.05 g. The experiment data were also fitted into kinetic, isotherm and thermodynamic models. The adsorption data fitted well with pseudo-second order model with the influence of intraparticle diffusion. For isotherm study, the data fitted well with Temkin model and the maximum capacity obtained was 150.8 mg/g. The thermodynamic studies proved that the adsorption of aspirin by TA-PEI is exothermic due to the negative enthalpy change value and it is spontaneous and feasible resulted from the negative value of Gibbs’ free energy change. The regeneration study was conducted and it was revealed that TA-PEI has the tendency to be regenerated with the maximum cycle of 5. In a nutshell, TA-PEI adsorbent was successfully synthesised and revealed an outstanding adsorption performance. Hence, TA-PEI was proved as a new promising adsorbent for the removal of aspirin.