Rice husk hydrochars from metal chloride-assisted hydrothermal carbonization as biosorbents of organics from aqueous solution

Yin Li,Hanxin Qian,Rongrong Chen,Genxing Pan,Shengdao Shan,Ruiqin Yang,Jing Di,Xikun Gai,Chengxing Mo,Fana Mulugeta Hagos

doi:10.1186/s40643-021-00451-w

Abstract

Hydrochar a carbon-rich material resulting from hydrothermal carbonization of biomass, has received substantial attention because of its potential application in various areas such as carbon sequestration, bioenergy production and environmental amelioration. A series of hydrochars were prepared by metal chloride-assisted hydrothermal carbonization of rice husk and characterized by elemental analysis, zeta potential, X-ray diffraction, Brunauer–Emmett–Teller measurements, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and scanning electron microscopy. The results reveal that the prepared hydrochars have carbon contents ranging from 45.01 to 58.71%, BET specific areas between 13.23 and 45.97 m2/g, and rich O-containing functional groups on the surfaces. The metal chlorides added in the feedwater could improve the degree of carbonization and show significant effects on the physical, chemical and adsorption properties of the hydrochars. The adsorption of the selected organics on the hydrochars is a spontaneous and physisorption-dominated process. The hydrochars possess larger adsorption capacities for 2-naphthol than for berberine hydrochloride and Congo red, and the modeling maximum adsorption capacities of 2-naphthol are in the range of 170.1–2680 mg/g. The adsorption equilibrium could be accomplished in 10, 40 and 30 min for 2-naphthol, berberine hydrochloride and Congo red, respectively. These results suggest metal chloride-assisted hydrothermal carbonization a promising method for converting biomass waste into effective adsorbents for wastewater treatment.

Highlights

Agricultural waste biomass is an abundant, renewable but still largely underutilized resource worldwide (Bian et al 2019)
The hydrochars prepared with metal chlorides added in the feed water display lower yields (28.97% to 47.02%) as compared to the hydrochar prepared in pure water (RHH, 47.10%), and the values decrease contrariwise to the concentration of the metal chlorides
The yield of the hydrochar prepared with monovalent salt KCl, divalent salt C aCl2 and trivalent salt FeCl3 added in the feed solvent at the same concentration does not present a linear correlation with the ionic strength of the feed solution, indicating that the yield of the metal chloride-assisted hydrochar is mainly affected by the metal salt type rather than the ionic strength of the medium, and the combined effect of the metal cation’s catalysis and solution acidity on biomass decomposition and hydrochar formation reactions may determine the final yield of the hydrochar

Summary

Introduction

Agricultural waste biomass is an abundant, renewable but still largely underutilized resource worldwide (Bian et al 2019). Adsorption has been widely applied in contaminant removal from water due to its cost effectiveness, high efficiency and easy operation (Jian et al 2018; Tong et al 2019). Hydrothermal carbonization can handle feedstocks with high moisture contents, and the liquid and gaseous products obtained from HTC procedure such as bio-oil and syngas could be utilized as fuels or the sources of platform molecules (Wang et al 2020). These make HTC a promising method of converting agricultural waste biomass into low-cost hydrochar adsorbents

Methods

Results

Conclusion