Economical way of Processing bio-char/activated Carbon from the wasteland weed Calotropis Gigantea and its Characterizations for Possible Applications

Abstract

There is a huge demand of energy in the whole world. Scientists and researchers are exploring various renewable biomass sources which are novel and can produce different forms of energy in addition to help mitigating environmental climate change, soil infertility and waste mismanagement problem. In order to cater these issues related to environment, soil and energy; biochar /activated carbon were processed through economical ways using renewable wasteland weed biomass resources in this work. In the present work, biomass of the different portions i.e. stem, leaf and flower of wasteland weed Calotropis Gigantea were carbonized individually between the temperature range 200°C to 900°C and percentage yield was estimated. Calotropis Gigantea bio-char obtained were characterised by yield, proximate analysis, CHNS analysis, bomb calorimetry analysis, Thermal Gravimetry Analysis (TGA) and Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Fourier Transform Infra-Red (FTIR) Spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), (Brunauer Emmett-Teller) BET surface area and pore size analysis. Presence of Carbon, Hydrogen, Nitrogen and Sulphur were confirmed from CHNS analysis. Based on the calorific value of bio-char obtained, it is found that it can be utilized as solid fuel. Thermal stability from TGA/DTA analysis leads to stability of bio-chars in soil. Presence of crystalline phase in biochar confirmed from XRD analysis. Further, with increase in carbonization temperature, cellulose crystalline peak of raw biomass was lost and formations of turbostratic carbon crystallites were confirmed from XRD analysis. Also, with increasing carbonization temperature, disordered band and graphitic band pattern of carbon became distinguishable as observed from RAMAN spectroscopy analysis. The bio-char surface is found to be porous based on SEM analysis. Presence of carbon and other elements in biochar is confirmed from EDS analysis. Surface functional groups found from FTIR analysis are helpful for adsorption of ions. Presence of lots of different dimension pores were also confirmed from FESEM analysis and thus this biochar can be used for adsorption purposes in different applications. Due to large pore size, BET surface area of the biochar was found less. The property of biochar depends on the composition, the type of biomass and the parameter of carbonizations. The temperature at which carbonization was done has huge influence on the characteristics and yield of the char. Based on the characterization analysis of carbonaceous residue (bio-char) obtained, it can be confirmed that use of such bio-chars can be potentially utilized for adsorption of ions and provide spaces for nutrients and water retention, increase soil fertility, act as source to sequester carbon in soil, mitigate climate change and reduce greenhouse gas emissions, helps in soil amendment for agricultural & environmental protection uses. There is huge demand of hierarchical porous activated carbon for use in energy storage devices and is a front-line area of research due to its versatile applications. Many attempts are being made to economise the process parameters to minimize the cost of production of activated carbon. Activated carbon (AC) from the wasteland biomass of Calotropis Gigantea stem was produced using chemical activating agent bleaching powder (CaOCl2) in the ratio of 0.5:1 and 1:1 of chemical and biomass at different activation temperatures of 400 oC, 600 oC and 900 oC in normal atmospheric conditions. Characterizations like XRD, FTIR, Raman Spectroscopy, FESEM, BET surface area and pore size analysis, HRTEM were done to find its suitability for application in Lithium/Sodium (Li/Na) ion batteries. Presence of graphitic structure was confirmed from XRD analysis. Functional groups found from FTIR analysis are active adsorption sites. Raman spectroscopy ordered graphitic structure is prerequisite for electrochemical performance. The highly porous activated carbon surface observed from vii FESEM analysis was further confirmed to have both mesopores and also micropores having appropriate surface area through BET surface area analysis. Highly porous activated carbon and crystalline graphitic structure found from HRTEM analysis makes it useful as an anode material for Li /Na ion batteries which are storage devices with high-energy density, long cycle life, safe operating and shelf life. Stem activated carbon made at 0.5:1 chemical impregnation had shown better properties than that of activated carbon made at 1:1 chemical impregnation. Therefore, in case of leaf and flower, chemical activation was done with bleaching powder (CaOCl2) at 0.5:1 (chemical:biomass) impregnation ratio at temperatures 400 oC, 600 oC and 900 oC in normal atmospheric conditions and were further characterized. Activated carbon from raw stem was prepared by using Potassium Carbonate (K2CO3) as chemical activating agent in the impregnation ratio of (0.5:1, 1:1 and 2:1) at 400 oC, 600 oC, 750 oC and 900 oC carbonization temperatures using normal atmosphere (NA) and in the impregnation ratio of (0.5:1, 1:1 and 2:1) at 600 oC, 750 oC carbonization temperatures in inert atmosphere (IA) of nitrogen at 100 ml/min. Further the effect of carbonization temperature and impregnation ratio of K2CO3 on the properties of activated carbons prepared under normal atmosphere and inert atmosphere were characterized and compared. While XRD analysis confirmed the presence of both disordered amorphous carbon humps and graphitic crystallite peaks. Ordered graphitic band increases with increase of impregnation but decreases with increase in carbonization temperature as studied from RAMAN spectroscopic analysis. Presences of functional groups found from FTIR analysis were more prominent in case of AC made in NA than that in IA. From FESEM study it was found that the micro porosity increases with increase of impregnation ratio and increase of activation temperature. But the porosity level attained at 400 oC carbonization temperature using NA was similar to that of obtained at 600 oC carbonization temperature using IA. BET surface area at 750 oC at chemical impregnation ratio 1:1 under NA was recorded highest (567.61 m2/g) containing both micropores and mesopores. The presence of micro and mesopores were further confirmed from HRTEM study. From the above analysis it can be stated that, NA activated carbons are preferable for different adsorption related applications and can be suitable for diversities of applications like batteries, fuel cells and supercapacitors. Therefore, CR2032 lithium coin-cell battery was fabricated using anode made out of activated carbon produced in this work and the electrochemical testing like cyclic performance, rate performance, Galvanostatic charge discharge (GCS), Cyclic-voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) study of CR2032 coin-cells were carried out and found that the produced activated carbon is suitable to be used as anode material for Li ion batteries. Hence in the present study, highly porous activated carbon was processed by economical way of processing from the wasteland weed Calotropis Gigantea and was found suitable for application in energy storage devices as an alternative to non-renewable sources to meet future energy demands.