From α-cellulose extracted from sugar cane bagasse, carboxymethyl cellulose (CMC), carboxymethyl cellulose acetate (CMCA) and carboxymethyl cellulose acetate butyrate (CMCAB) have been prepared, characterized and evaluated by TGA and DSC. TGA decomposition curves of CMCAB showed three decomposition stages, while cellulose, CMC and CMCA revealed two decomposition stages. The TGA of cellulose and CMC showed residual weight of 19.6 and 34.2%, respectively, at 600 °C, which indicates the presence of a fraction of non-volatile components. Meanwhile, the residual weight of CMCA and CMCAB was very low, which indicates their high purity. The activation energy and thermal stability of CMCAB were higher than those of the other derivatives due to the decomposition of the amorphous part during the modification. The DSC curves showed that CMCAB is a glassy thermoplastic material with glass transition temperature of 138.35 °C, whereas endothermic melting was found at 200 °C.

Fluorescent carbon quantum dots (CQDs) were prepared by an economical, green, and single-step procedure with the assistance of microwave heating of urea with bagasse (SCB), cellulose (C), or carboxymethyl cellulose (CMC). The prepared CQDs were characterized using a series of spectroscopic techniques, and they had petite size, intense absorption in the UV, and excitation wavelength-dependent fluorescence. The prepared CQDs were used for Pb(II) adsorption from an aqueous solution. The removal efficiency percentages (R %) were 99.16, 96.36, and 98.48% for QCMC, QC, and QSCB, respectively. The findings validated the efficiency of CQDs synthesized from CMC, cellulose, and SCB as excellent materials for further utilization in the environmental fields of wastewater pollution detection, adsorption, and chemical sensing applications. The kinetics and isotherms studied found that all CQDs isotherms fit well with the Langmuir model than Freundlich and Temkin models. According to R2, the pseudo-second-order fits the adsorption of QCMC, while the first-order one fits with QC and QSCB.

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The chromium adsorption behavior from aqueous solution by the amphoteric Janus nitrogen-doped carbon quantum dots (AJ–N–CQDs) was investigated. The pseudo-first-order and the second-order adsorption kinetics models were employed to analyze the experimental data; the second-order adsorption kinetics model presented a better correlation to the experimental data, suggesting a chemisorptions process. The values obtained in the pseudo-first-order are still suitable for describing the Kinetics of Cr(VI) sorption. These values elucidate the surface processes involving chemisorption and physisorption in the adsorption of Cr(VI) by AJ–N–CQDs. The R2 of the Boyd model gave a better fit to the adsorption data of AJ–N–CQDs (i.e., external diffusion), which means the surface processes involving external Cr(VI) adsorption by AJ–N–CQDs. The higher value of α may be due to the greater surface area of the AJ–N–CQDs for the immediate adsorption of Cr(VI) from the aqueous solution. AJ–N–CQDs have fluorescence spectra before and after Cr(VI) adsorption, indicating they are promising for chemical sensor applications.

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