Table 4 Summary of IR absorptions in raw biomass and hydrochars

From: Production and characterisation of adsorbents synthesised by hydrothermal carbonisation of biomass wastes

Adsorbent Wavelength (cm−1) Functional group Interpretation
Raw biomass Hydrochar
Coco-peat 3333.81 3341.97 O–H Indicates the presence of hydroxyl, water, alcohols due to cellulose, phenols and lignin
2917.39 2937.81 C–H Indicates the presence of alkane suggesting methyl and methylene groups
1606.85 1605.44 C=C Presence of aromatic rings due to lignin
1235.45 1031.97 C–O Due to vibration from ethers, phenols, aliphatic alcohols
512.87 C–Br Alkyl halide
Coconut shell 3343.69 3344.51 O–H Presence of hydroxyl, water, alcohols due to cellulose, phenols and lignin
2929.98 2931.14 C–H Small peaks due to absorption from CH bond of aliphatic carbon, methylene, and methyl groups
1724.74 1603.93 C = O The vibration due to the esters, carboxylic acids or aldehydes or ketone present in the cellulose and lignin
1239.92 1027.45 C–O Presence of ethers, phenols, aliphatic alcohols
1031.76 C–O–H Means there is deformation in cellulous
Rice husk 3333.93 3398.71 N–H Occurrence of OH, carboxyl and amine groups due to high formation of amide in the hydrochar
2917.65 C–H Small peaks due to absorption from CH bond of aliphatic carbon, methylene, and methyl groups
1634.66 1616.90 C=O Aliphatic C–H stretching
1032.83 1030.54 C–O–H Means there is deformation in cellulose
783.68 788.07 Si–O Indicates the vibration of silica
Lemon peel 3289.52 3338.11 O–H Hydroxyl, carbohydrate and lignin. Indicates the presence of constituents such as protein, pectin and cellulose
2919.26 2917.57 C–O–R Presence of esters
1606.87 1609.01 C = O Aromatic skeletal vibration
600.95 C–Cl Alkyl halide
Eggshell 3278.58 OH Hydroxyl, carbohydrate, and lignin. Indicates the presence of constituents such as protein, pectin, and cellulose
1793.61 1796.06 C=O The vibration due to the presence of esters, carboxylic acids or aldehydes and ketone
1393.63 1393.63 CH3 bend Aliphatic C–H stretch in CH3
871.16 871.10 C–F Presence of aromatic ring
711.98 712.13 C–Br Presence of aromatic ring