Influence of ammonium salts and temperature on the yield, morphology and chemical structure of hydrothermally carbonized saccharides

Kenneth G Latham,Adam Ferguson,Scott W Donne

doi:10.1007/s42452-018-0055-2

Kenneth G Latham, Adam Ferguson + Show 1 more

Open Access

https://doi.org/10.1007/s42452-018-0055-2

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Abstract

In this work, the influence of (NH4)2SO4 and (NH4)2HPO4 as well as temperature is examined on the hydrothermal carbonization of glucose, fructose and sucrose. Increasing the temperature from 160 to 220 °C increased the yield of hydrothermal carbon for each saccharide for the (NH4)2SO4 solution, whereas (NH4)2HPO4 produced a yield that was independent of temperature. The addition of (NH4)2SO4 increased the yield obtained at 220 °C by 4.27, 7.03 and 2.01 wt% for glucose, fructose and sucrose over the baseline salt free solution, respectively. (NH4)2SO4 also increased the quantity of acid produced and the average size of the hydrothermal carbon spheres. Conversely, (NH4)2HPO4 produced carbon structures consisting of interlocked spherical shapes and produced almost no acidic products. XPS analysis revealed that (NH4)2SO4 incorporated nitrogen and sulfur into the hydrothermal structure, while (NH4)2HPO4 only allowed nitrogen to be incorporated. It was assessed that NH4+ enhances the production of hydrothermal carbon, except in the presence of PO43−, which prevents the reaction from effectively forming hydrothermal carbon and organic acids.Graphical abstract

Highlights

Hydrothermal carbonization has gained significant interest over the last 10 years for its ability to synthesize functionalized carbon materials at low temperatures (150–350 °C) from a wide variety of carbon precursors [1,2,3,4,5]
The hydrothermal carbons (HTC) yield for glucose remained below 6 wt% until the temperature was raised 220 °C, in which the yield rose to 21 wt%
The hydrothermal carbonization of glucose, fructose and sucrose under different temperatures and ammonium salts produced a wide range of yields, sizes and chemical morphologies depending on the temperature and ammonium salt added

Summary

Introduction

Hydrothermal carbonization has gained significant interest over the last 10 years for its ability to synthesize functionalized carbon materials at low temperatures (150–350 °C) from a wide variety of carbon precursors [1,2,3,4,5]. The addition of dopants into the carbon structure (i.e., nitrogen, phosphorus and sulfur) have been shown to enhance the properties of hydrothermal carbons in electrochemical capacitors [13, 14] and oxygen reduction catalysts [20] It is for this reason that examining the effects of various dopants and additives is important to understanding their influence on hydrothermal carbonization and the resultant carbonaceous product

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