This research deals with the effect of the temperature on the physical, thermal, electrochemical, and adsorption properties of the carbon micro-spheres using hydrothermal carbonization (HTC). Until recently, limited research has been conducted regarding the effects of delignification during the HTC process of biomass residues especially Dimocarpus longan. In this regard, lignin was first extracted from the lingo-cellulosic waste of Longan fruit peel (Dimocarpus longan). The holocellulose (HC) separated from lignin and raw biomass substrates (Longan fruit exocarp/peel powder, LFP) were carbonized at different temperatures using water as the green catalyst. Hydrothermal carbonization (HTC) was performed for both of the samples (LFP and HC) at 200 °C, 250 °C, and 300 °C for 24 h each. The surface morphological structures, the porosity, and the Brunauer-Emmett-Teller (BET) surface area of the prepared micro-spherical carbon were determined. The BET surface areas obtained for HC-based carbon samples were lower than that of the raw LFP based carbon samples. The carbon obtained was characterized using ultimate and proximate analyses. The surface morphological features and phase transformation of the synthesized micro-spherical carbon was characterized by a field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analysis. The results demonstrated that the extraction of lignin could significantly alter the end properties of the synthesized carbon sample. The carbon spheres derived from LFP showed a higher carbon content than the HC-based carbon. The absence of lignin in the holo-cellulose (HC) made it easy to disintegrate in comparison to the raw, LFP-based carbon samples during the HTC process. The carbonaceous samples (LFP-300 and HC-300) prepared at 300 °C were selected and their adsorption performance for Pb (II) cations was observed using Langmuir, Freundlich, and Temkin linear isotherm models. At 30 °C, the equilibrium data followed the Langmuir isotherm model more than the Freundlich and Temkin model for both the LFP-300 sample and the HC-300 sample. The potential of the synthesized carbon microspheres were further analyzed by thermodynamic characterizations of the adsorption equilibrium system.

A cost-effective, facile hydrothermal approach was made for the synthesis of SnO2/graphene (Gr) nano-composites. XRD diffraction spectra clearly confirmed the presence of tetragonal crystal system of SnO2 which was maintaining its structure in both pure and composite materials’ matrix. The stretching and bending vibrations of the functional groups were analyzed using FTIR analysis. FESEM images illustrated the surface morphology and the texture of the synthesized sample. HRTEM images confirmed the deposition of SnO2 nanoparticles over the surface of graphene nano-sheets. Raman Spectroscopic analysis was carried out to confirm the in-plane blending of SnO2 and graphene inside the composite matrix. The photocatalytic performance of the synthesized sample under UV irradiation using methylene blue dye was observed. Incorporation of grapheme into the SnO2 sample had increased the photocatalytic activity compared with the pure SnO2 sample. The electrochemical property of the synthesized sample was evaluated.

The formation of uniform dielectric barrier discharges (DBDs) under atmospheric pressure is a remarkable achievement with the addition of electronegative gasses in closed reactors. This work is the part of dielectric barrier discharge achieved under atmospheric pressure. A uniform glow discharge is produced in capacitive discharge reactor. An alternating voltage source (0-2.5) kV having frequency of 50Hz is applied across the two parallel disc electrodes. A couple of dielectrics (glass) used as a discharge barriers one on each electrode. The oxygen gas injected into the reactor controlled by mass flow controller with flow rate 30ml/min. The current-voltage waveforms for oxygen discharge achieved, fulfilling the basic conditions of discharge homogeneity. The diagnostic techniques rely on electrical discharge method and power balance method to differentiate discharges and estimate the electron density for different values of applied voltages. A significant relation is found indicating the variation of electron density with applied voltage.