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• The structural differences of biomass had significant influence on pyrolysis mechanism. • Cleavage of glycosidic bond and dissociation of O-acetyl group in softwood hemicellulose were prone to occur. • The breakage of α-ether bond of hemicellulose-lignin bonds mainly occurred via Cα-O concerted cleavage. Biomass pyrolysis involves complex structural changes and numerous chemical reactions. At present, most studies on actual biomass pyrolysis focus on the macroscopic thermal degradation process, while the studies on microscopic pyrolysis rules are still very limited. This work provides a new insight into the pyrolysis mechanism of three types of actual biomass, namely hardwood (eucalyptus saligna), softwood (pinus sylvestris) and straw (corn straw), by combining in-situ characterization of the evolution of biomass structures with density functional theory (DFT) calculations of pyrolysis pathways. Firstly, the evolution of various characteristic structures during biomass pyrolysis was monitored by in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFT). It was found that the thermal stability of the same functional group in different biomass samples are not exactly the same, and the structural differences in biomass would lead to different pyrolysis behaviors. Then, considering the great structural difference of hemicellulose in different biomass, the key initial pyrolysis reaction paths including the cleavage of glycosidic bonds, the dissociation of side chains and the opening of sugar ring of hemicellulose were studied by DFT calculations. It was found that the cleavage of glycosidic bonds and the dissociation of O-acetyl side chains of glucomannan in softwood hemicellulose are more advantageous than those of xylan in hardwood and straw hemicellulose. In addition, the cleavage mechanism of hemicellulose-lignin bond (LC), a characteristic connection structure between different components of actual biomass, was investigated. The result showed that the cleavage of Cα-O mainly occurred by concerted mechanism for α-ether bond of LC. [ABSTRACT FROM AUTHOR]

In industrial pollutants, phenol is a kind of degradation-resistant hazardous compound. It is generated during industrial processes in factories and treatment at sewage plants. In this study, we analyse the photocatalytic activity of TiO2 and rGO as a composite for the degradation of phenol. Hybridised titanium dioxide/reduced graphene oxide (TiO2/rGO) nanocomposites were synthesised by a simple hydrothermal method using flake graphite and tetrabutyl titanate as raw materials. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer–Emmet–Teller (BET) specific area analysis, Fourier transform infrared spectroscopy (FTIR), Raman, X-ray photoelectron spectroscopy (XPS), photoelectrochemical analysis, and UV–vis diffuse reflectance spectra (DRS) were employed to characterise the physicochemical properties of the as-prepared nanocomposites. The results showed the TiO2/rGO nanocomposites' significant anatase phase and a small fraction of the rutile phase the same as that of the as-prepared TiO2 nanoparticles. The spherical TiO2 nanoparticles (diameter 20–50 nm) were agglomerated slightly and the agglomerates were anchored on the rGO sheets and dispersed symmetrically. The specific surface area of TiO2/rGO-4% nanocomposites was 156.4 m2/g, revealing a high specific surface area. Oxygen-containing functional groups that existed in TiO2/rGO-4% nanocomposites were almost removed during hydrothermal processing. The photocurrent response of TiO2/rGO-4% was strongest among the TiO2/rGO nanocomposites, and the bandgap of TiO2/rGO-4% was 2.91 eV, showing a redshift of absorption into the visible region, which was in favour of the high photocatalytic activity of TiO2/rGO nanocomposites under visible light (λ > 420 nm). Moreover, the samples were employed to photodegrade phenol solution under visible light irradiation. TiO2/rGO-4% nanocomposite degraded the phenol solution up to 97.9%, and its degradation rate constant was 0.0190 h−1, which had higher degradation activity than that of other TiO2/rGO nanocomposites. This is a promising candidate catalyst material for organic wastewater treatment. [ABSTRACT FROM AUTHOR]

Cellulose is one of the major components of biomass. The study on its pyrolysis process will be beneficial to the in-depth understanding of biomass pyrolysis mechanism. In this work, in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFT) combined with two-dimensional perturbation correlation infrared spectroscopy (2D-PCIS) was first used to characterize the evolution process of the functional groups in cellulose during pyrolysis. The results showed that the degradation of carbon skeleton was prior to the dehydration of free hydroxyls after the destruction of hydrogen bond networks during pyrolysis. The thermal stability of C O in cellulose followed by the order of glycosidic bond