Abstract
Surface structure and chemical properties of adsorbents are important factors required to understand the mechanism of adsorption. The purpose of this study was to produce hydrochars from biomass using hydrothermal carbonisation (HTC) and to analyse their sorption capacities. The biomass used in this study were coco-peat (CP), coconut shell (CS), eggshell (ES), rice husk (RH) and lemon peel (LP). The operating conditions for HTC were 200 °C and 20 h residence time. The characterisation methods consisted of Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Fourier Transform Infrared Ray (FTIR) Spectroscopy, and Brunauer, Emmett and Teller (BET). The results showed that HTC improved the sorption capacities of the biomass wastes. It was found that hydrochars were crispy and flaky with more micro- and meso-porous structures, indicating that lignin and other components were denatured due to carbonisation. This led to the creation of more active sites for sorption and pollutant binding. The hydrochars showed a percentage increase in carbon content and a decrease in oxygen content with traces of other elements, compared to their corresponding raw biomass. The major functional groups identified were –OH and –COOH. The surface area of the hydrochars which include CP (2.14 m2/g), CS (14.04 m2/g), ES (0.50 m2/g), RH (15.74 m2/g), and LP (6.89 m2/g) were significantly improved compared with those of the raw biomass. The study showed that the hydrochars produced from the biomass wastes have the potential to be used as adsorbents.
Highlights
Micro and macro structural properties, elemental composition, functional groups and surface area, pore volume as well as pore size are important factors required in order to understand the intrinsic properties that underpin adsorption of organic and inorganic pollutants onto material surface
The samples were degassed in a vacuum set at a heating rate of 10 °C/min up to a temperature of 110 °C, and kept overnight for 16 h by following the method described by Pilon et al [23]
This study revealed that higher meso-pore was obtained in the range of 1.0–4.0 ml/g, indicating an onset of the porous structure with dominating pore diameter at approximately 3.0 ml/g for the hydrochars of coconut shell, rice husk and lemon peel; while the remaining hydrochars produced nonporous or macro-porous materials characterised by weak affinity between adsorbent and adsorbate and within the molecules as well
Summary
Micro and macro structural properties, elemental composition, functional groups and surface area, pore volume as well as pore size are important factors required in order to understand the intrinsic properties that underpin adsorption of organic and inorganic pollutants onto material surface. This research provides a simple, efficient, sustainable, and affordable technique for producing adsorbents from biomass waste through a thermochemical process called hydrothermal carbonisation (HTC). Activated carbon has proven to be very effective in the removal of organic and inorganic contaminants in the food industry and wastewater treatment plants. They are used in the purification of sugar; decolouration of syrups, wine, vinegar, removal of methylene blue and other types of dyes [9]. The application of activated carbon is limited by the high production cost partly due to the pyrolysis process and the treatment to obtain the activated carbon [12] This limitation has led into research for a simpler and costeffective technique to carbonise biomass waste. Majority of the organic components are transferred to the liquid phase [14]
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