Inorganic Salt Catalysed Hydrothermal Carbonisation (HTC) of Cellulose

The presence of inorganic salts either as part of the substrate or added to the reaction medium are known to significantly affect the reaction pathways during hydrothermal carbonisation (HTC) of biomass. This work aims to understand the influence of salts on hydrothermal carbonisation by processing cellulose in the presence of one or more inorganic salts with different valency. Batch experiments and Differential Scanning Calorimetry were used to investigate the change in reaction pathways during hydrothermal conversion. The effect of salts on the rate of HTC of cellulose can be correlated with the Lewis acidity of the cation and the basicity of the anion. The effect of the anion was more pH-dependent than the cation because it can protonate during the HTC process as organic acids are produced. The introduction of salts with Lewis acidity increases the concentration of low molecular weight compounds in the process water. The addition of a second salt can influence the catalytic effect of the first salt resulting in greater levulinic acid yields at the expense of hydrochar formation. Salts also play an important role in cellulose dissolution and can be used to modify the yield and composition of the hydrochars.

Mesoporous Carbon from Optimized Date Stone Hydrochar by Catalytic Hydrothermal Carbonization Using Response Surface Methodology: Application to Dyes Adsorption

Providing efficient and environmental friendly ways to recover lignocellulosic waste remains a challenge around the world. In this study, citric acid-catalyzed hydrothermal carbonization (CHTC) was coupled with pyrolysis to convert date seed (Ds) into adsorbent material. In this regard, a central composite design (CCD) using response surface methodology (RSM) was developed to examine the influence of temperature, reaction time, and catalyst dose on the mass yield (Ym(%)) and carbon retention rate (CRR(%)) in the produced hydrochars. The optimized hydrochar (OHC-Ds) was obtained under optimal conditions (200°C, 120 min, 20 mg) and characterized by a Ym(%) and CRR(%) of 59.71% and 75.84%, respectively. Chemical activation by KOH of OHC-Ds followed by pyrolysis at 600°C resulted in an active material (AOHC-Ds) rich in carbon and characterized by a high specific surface area of 1251.5 m2/g, with the dominance of mesopores, as well as an amorphous structure comparable to graphite shown by X-ray diffraction (XRD) analysis. Adsorption experiments of two dyes on AOHC-Ds showed a high maximum adsorption capacity (Qm) of 657.89 mg g−1 for methylene blue (MB) and 384.61 mg g−1 for methyl orange (MO) compared to other conventional adsorbents. This result is due to the low acidity (pHpzc) of the surface of AOHC-Ds, which equals 6.75, and its surface, which is also rich in oxygenated functional groups such as (-OH), (C=O), and (C-O) shown by FTIR analysis. These results suggest that the coupling of CHTC and KOH activation followed by pyrolysis is an encouraging way to prepare an efficient and inexpensive adsorbent to remove dyes in wastewater.

Enhanced adsorptive removal of sulfamethoxazole from water using biochar derived from hydrothermal carbonization of sugarcane bagasse

This research work primarily focussed on the production of biochar from sugarcane bagasse through HTC followed by NaOH activation at inert atmosphere for removing SMX from water. The biochar was characterized for structural morphology and presence of functional groups. XRD and FTIR analysis confirmed that presence of aromatized graphitic structure accumulated with oxygenated functional groups are responsible for the elimination of SMX. SEM analysis portrayed the sphere-shaped structure of biochar with hydrophobic groups interior and hydrophilic groups exterior. BET isotherm revealed the active surface area equal to 1099 m²/g with high coverage of mesopores structure. P_zpc of adsorbent is evaluated to 6.5 stating that effective removal of SMX depends on ionization effects induced due to reaction medium. Kinetics study revealed the sorption of SMX followed chemical interaction pertaining to Elovich model. Isotherm studies revealed that Freundlich model fitted well stating heterogeneous mode of interaction. Immobilization of SMX on surface of ABC is due to charge assisted hydrogen bonding and π-π interaction with graphitized carbon, showing maximum sorption capacity of 400 mg/g through spontaneous reaction. The results suggested that HTC derived biochar had great adsorption affinity with respect to pH towards SMX and could be employed as an effective sorbent in cleaning water contaminants.

Remarkable Physical and Thermal Properties of Hydrothermal Carbonized Nanoscale Cellulose Observed from Citric Acid Catalysis and Acetone Rinsing

Citric acid (CA) was used for the hydrothermal carbonization (HTC) of cellulose nanofiber and found to exert remarkable effects on the chemistry and physical aspects of the product distribution. More specifically, the morphology, yield, elemental and proximate composition, chemical functional groups, thermal properties and surface properties of the resultant hydrochars were studied extensively. The morphological properties of the final char were the singularly most surprising and unique finding of this study. The cellulose nanofiber hydrochars were contrasted to hydrochars from bleached softwood pulp, having a similar composition with the former, to pinpoint the role of nano-dimensions. Without the presence of CA, the pulp hydrochar lacked several of the spherical dimensions shown in the nanocellulose; however, and unexpectedly, the presence of CA caused a homogenization of the final product distribution for both samples. Finally, thermally stable and high surface area hydrochars were obtained when the hydrochar was rinsed with acetone.

Hydrothermal Synthesis of Cellulose-Derived Carbon Nanospheres from Corn Straw as Anode Materials for Lithium ion Batteries

As a most attractive renewable resource, biomass has the advantages of low pollution, wide distribution and abundant resources, promoting its applications in lithium ion batteries (LIBs). Herein, cellulose-derived carbon nanospheres (CCS) were successfully synthesized by hydrothermal carbonization (HTC) from corn straw for use as an anode in LIBs. The uniform distribution and cross-linked structure of carbon nanospheres were obtained by carefully controlling reaction time, which could not only decrease the transport pathway of lithium ions, but also reduce the structural damage caused by the intercalation of lithium ions. Especially, obtained after hydrothermal carbonization for 36 h, those typical characteristics make it deliver excellent cycling stability as well as the notable specific capacity of 577 mA h g-1 after 100 cycles at 0.2C. Hence, this efficient and environment-friendly method for the fabrication of CCS from corn straw could realize the secondary utilization of biomass waste, as well as serve as a new choice for LIBs anode materials.

Facile one‐pot hydrothermal synthesis of stable and biocompatible fluorescent carbon dots from lemon grass herb

Luminescent carbon‐based nanomaterials hold great promise due to their stable photo‐physical behaviour, biocompatibility and lower toxicity. This work involves economic and facile one‐pot green synthesis of water‐soluble nanostructures from lemon grass (LGNS) [Cymbopogon citratus (DC) Stapf ] as carbon source. High‐resolution transmission electron microscopy confirmed the formation of LGNS with lattice spacing of 0.23 nm matching low‐dimensional graphitic structures. The strong absorption exhibited at 278 nm could be attributed to л‐states of sp2 /sp3 hybridisation in carbon nanostructures. Fluorescence spectroscopy of LGNS exhibited strong excitation‐dependent emission properties over a broad range of wavelengths from 300 to 600 nm. Quantitatively, these LGNS were estimated to have quantum yield of 23.3%. Biomass derived LGNS could be potentially exploited for wide variety of applications like bioimaging, up‐conversion, drug delivery and optoelectronic devices. To this extent, synthesised LGNS were used to image yeast cells via multicolour/multi‐excitation fluorescence imaging.

Depositing CdS nanoclusters on carbon-modified NaYF4:Yb,Tm upconversion nanocrystals for NIR-light enhanced photocatalysis

High-quality hexagonal NaYF4:Yb,Tm upconversion nanocrystals (UCNs) prepared in organic solutions display uniform sizes and strong UC emissions, but they possess a hydrophobic surface which hinders combining them with various semiconductor nanocrystals (NCs) to form a hybrid NIR-activated photocatalyst. Herein we present a facile approach to modify hydrophobic UCNs with a uniform carbon layer and enable them with hydrophilicity and surface functionalization. The carbon shell provides a good substrate for enriching with metal ions and in situ generation of CdS nanoclusters on the particle surface which can utilize both the upconverted UV and visible emissions. The developed NaYF4:Yb,Tm@C@CdS nanoparticles are characterized with TEM, SEM, XRD, PL and UV-Vis spectra and their formation mechanism is elucidated. The products display good photocatalytic activity under visible light and obviously enhanced performance under Vis-NIR light, due to the efficient utilization of UC emissions and the strong adsorption capacity of the carbon shell. The working mechanism of the hybrid photocatalysts is also proposed.