Lignocellulosic waste-derived hydrochar@bimetallic composites via hydrothermal carbonization for rapid and reusable...

Design and development of bio-waste (especially ligno-cellulosic) driven composite materials with transition metal oxides for high entropic materials with efficient charge transfer capacity and surface catalytic properties have received lot of interest. Herein, three environmentally benign and efficient ligno-cellulosic pine needle derived hydrochar composite materials with bimetallic oxides were isolated via in-situ hydrothermal carbonization at 180 °C for 24 h. The three hydrothermally isolated composite materials, PNHC-1 (Fe-Co@HC), PNHC-2 (Co-Ti@HC), and PNHC-3 (Fe-Ti@HC) were comprehensively studied using various physicochemical and structural analysis tools. These included optical absorption spectroscopy (UV-Visible), vibrational spectroscopy (FT-IR), Raman spectroscopy, surface imaging (FE-SEM) and elemental profiling, crystallographic analysis (XRD), surface chemical state evaluation (XPS), and porosity and surface area (BET) measurements. For potential application, all the material were employed as adsorbent cum photocatalyst for degradation of both cationic (Crytal violet (CV), malachite green (MG)) and anionic (Congo red (CR)) dyes under UV-light (9 W) as well as visible light photo-degradation. The various degradation experiments clearly delineated that all the material possesses a superior capacity in lieu of the three dyes for efficient photocatalytic dye degradation. Moreover, PNHC-2 labelled bimetallic hydrochar composite outperformed other materials in terms of efficacy of dye removal of more than 95 % for more than 5 cycles. However, it is worth mentioning here that all the three hydrochar@bimetallic composite hetero-junctions (PNHC-1, PNHC-2, PNHC-3) showed a remarkable efficacy in dye removal rates of 95.75 %, 92.97 %, 94.41 % for CV, 80 %, 94.41 %, 92.81 % for MG, and 90 %, 95 %, 91.54 % for CR, respectively for 50 ppm dye concentration in 60 min. Degradation kinetics revealed a strong linear correlation adheres to a pseudo-first-order kinetic model following modified Langmuir-Hinshelwood (L-H) mechanism in all cases, suggesting heterogeneous photocatalytic reactions. The value of correlation coefficient i.e. R² of PNHC-2 for CV, MG, CR are 0.9764, 0.958, and 0.95604 respectively. Our results suggested that ligno-cellulosic waste, especially pine needles, that causes forest fires could be used as potential substitute for multifunctional materials towards their use in water pollution remediation effectively, delineating the potential for sustainable development.