(2ie) Electronic Waste Derived Three-Dimensional Carbon Aerogel for the Adsorption of Phenol from Wastewater

Introduction

Petrochemical industries and refineries are considered the backbone of a developing nation’s economy. However, growing environmental concern and stringent pollution control norms have affected their long-term sustainability. Thus, it is essential to find economical and affordable solutions to control pollutants generated from the industries and refineries. Phenol and its derivatives are the major pollutants present in the petrochemical refinery wastewater [1]. Electronic waste is increasing with staggering annual rate of 4%−5% globally and electronic waste generated in 2019 was approximately 53.6 million metric tons [2]. Hence this waste material has been used for the treatment of wastewater. In the present study, we have employed the novel, highly porous, and hydrophobic hybrid aerogel of the carbon derived from electronic waste using the freeze-drying process. The carbon material from the electronic waste was obtained using the pyrolysis and ultrasonication process and the methodology is reported in our published article [3]. The hybrid aerogel thus formed is utilized to remove phenol one of the major pollutants in industrial effluents. The novel aerogel derived performed excellently for the removal of phenol and showed 95% removal efficiency respectively. The structure of aerogel is analysed by field emission scanning electron microscope, transmission electron spectroscopy, Fourier transform infrared spectra and N2 adsorption and desorption experiment. ANOVA analysis based on the central composite design-response surface methodology (CCD-RSM) showed a good fit between quadratic model predictions with experimental values, thus resulting in R² of 0.9992 for phenol. Furthermore, adsorption behaviour, including kinetics, isotherms, and thermodynamics, are systematically investigated. The thermodynamic study also signifies a favourable and spontaneous removal process. Subsequently, the effect of adsorbent dosage, phenol concentration, contact time, and pH on phenol removal from the wastewater were studied. The adsorption mechanism of phenols with the synthesized aerogel is also well studied. The results obtained confirm that the synthesized aerogel is an effective medium to remove phenols from industrial wastewater effectively.

Keywords: Petrochemical refineries, Pollution, electronic-waste, Phenols, Wastewater treatment

Materials and Methods

Printed circuit board (Computer mother board) was taken as raw material for this process. The raw material was directly pyrolyzed in a pilot plant and along with solid some gas and liquid by products were also formed which will also be analyzed for their use in energy generation. The solid material was then ultrasonicated followed by treatment with aqua regia for the removal of metals. The resulted product was mixed with carboxy methyl cellulose and heated hydrothermally, and the resulted gel type material was freeze dried at -50 ᵒC. The resulted aerogel was then activated using KOH (1:5) at 700 ᵒC.

Results and Discussion

Three different types of aerogels were formed by taking the different mass ratio of carbon and carboxymethyl cellulose (1:05, 1:1 and 1:2) and thoroughly characterized by using scanning electron microscopy, HRTEM, FT-infrared spectroscopy, X-ray diffraction and Raman spectroscopy. Results showed that the aerogel of 1:1 mass ratio was found to be better then the others and was used for the adsorption of phenol in batch as well as column study. Batch adsorption results showed that the synthesized aerogel showed 141 mg/g adsorption capacity while the column study showed that the aerogel has around 39 mg/g adsorption capacity which needs to modify further using some experiments. The batch adsorption data was fitted in two and three parameter models such as Langmuir, Freundlich, Temkin, Sips and Tooth while for the kinetic study the data was fitted in pseudo first order model, pseudo second order model and elovich model. For the column study, effect of bed height, initial concentration and flow rate were studied and Yan, Yan and Nelson, Bohr-Adams model were applied to investigate the applicability of the experiment.