Jalli Ramesh Babu

Cadmium is one of the most toxic heavy metal ions found in wastewaters and its remedial methods are globally investigated. Removal methods based on biomaterials as adsorbents are proving to be simple, effective and eco-friendly. In the present investigation, bio-adsorbents derived from Cochlospermum regium plant stems (CRSP) and its active carbon (CRAC) are observed to have good adsorption for toxic cadmium ions. Hence, extraction conditions are optimized for maximum Cd-extraction: 55.0% with ‘CRSP’ and 70.0% with ‘CRAC’, from Cd²⁺ solutions of concentration: 25.0 mg/L. The adsorption capacities are 6.9 mg/g with CRSP and 12.6 mg/g with ‘CRAC’. When ‘CRAC’ is impregnated with nano-CeO₂ (CRAC.nCeO₂) and is used as adsorbent, the percentage of Cd-extraction is increased to 90.0% and adsorption capacity to 22.5 mg/g at the optimized extraction conditions. To overcome the agglomeration of nanoparticles, the ‘CRAC.nCeO₂’ is immobilized in Zr-alginate beads and thus obtained beads are investigated as adsorbent. With beads (CRAC.nCeO₂–Zr.alg), the percentage of Cd-adsorption is enhanced to 95.0% and adsorption capacity to 24.6 mg/g. The adsorbents are characterized by adopting XRD and FTIR techniques. The adsorption mechanism is assessed by evaluating thermodynamic parameters, isotherm and kinetic models. The thermodynamic parameters and FTIR spectral characteristics indicate the formation of ‘surface complex’ between Cd²⁺ and adsorbent’s functional groups. The adsorption follows Freundlich isotherm and pseudo-second order model. Many co-ions have not effected the percentage of extraction and interestingly, the presence of some cations (Al³⁺ and Fe³⁺) have synergistically enhanced the Cd-extraction. Spent sorbents can be regenerated and reused with marginal loss of adsorption capacity. The adsorbents developed are successfully used to treat real Cd-polluted wastewater. The novelty of the present investigation is that the effective, eco-friendly, renewable and robust sorbents with high sorption capacities are developed for Cd-remediation of water. Graphical Abstract The merit of the present investigation is that adsorbents with high sorption capacities, are developed based on bio materials of Cochlospermum regium and nano-CeO₂. Zirconium alginate beads doped with nano-CeO₂ and active carbon of Cochlospermum regium stems, are found to be highly effective for Cd-removal and spent adsorbent can be regenerated and re-used for five cycles.

The effect of doping nano Sm2O3 particles in PVA + Na3C6H5O7 (90:10% w/w) polymer composite films on the structural, thermal, electrical properties and battery parameters are investigated. The PVA + Na3C6H5O7 + nano Sm2O3 (90:10:1- 4% w/w) films were synthesized and characterized. A 2% w/w Sm2O3 film was relatively homogeneous with high amorphous in nature enabled the movement of nanoparticles in the matrix of polymer under potential gradient. The maximum conductivity was 2.09 × 10-3 S cm-1 for 2% w/w nano Sm2O3 film and it is 7 orders more than polyvinyl alcohol. The films were adopted in batteries with configuration: Anode (Mg+MgSO4)/[{PVA:Na3C6H5O7 (90:10% w/w)} + nano Sm2O3 (1-4% w/w)]/cathode (iodine + carbon + pieces of electrolyte) and battery parameters were assessed. The discharge time is 174 h with the cell having 2.0% w/w nano Sm2O3 film. These nano Sm2O3 doped films are successfully adopted in the fabrication of batteries and also the proposed cells are simple, effective, eco-friendly and economical.

Varying concentrations of nano-Pr₂O₃ doped in “PVA + Sodium Citrate (90 : 10)” polyelectrolyte films are synthesized using solution cast technique and the films are characterized adopting FTIR, XRD, SEM, and DSC methods. The film with 3.0% of nano-Pr₂O₃ content is more homogenous and possesses more amorphous region that facilitate the deeper penetration of nanoparticles into the film causing more interactions between the functional groups of the polymeric film and nano-Pr₂O₃ particles and thereby turning the film more friendlily to the proton conductivity. The conductivity is maximum of 7 × 10⁻⁴ S/cm at room temperature for 3.0% nano-Pr₂O₃ film and at that composition, the activation energy and crystallinity are low. With increase in temperature, the conductivity is increasing and it is attributed to the hopping of interchain and intrachain ion movements and furthermore decrease in microscopic viscosity of the films. The major charge carriers are ions and not electrons. These films are incorporated successfully as polyelectrolytes in electrochemical cells which are evaluated for their discharge characteristics. It is found that the discharge time is maximum of 140 hrs with open circuit voltage of 1.78 V for film containing 3% of nano-Pr₂O₃ and this reflects its adoptability in the solid-state battery applications.

Composite polymer electrolyte films containing various concentrations of nano‐Dy₂O₃ (1.0 to 4.0%) in PVA + sodium citrate (90 : 10) are synthesized adopting solution cast method and are characterized using FTIR, XRD, SEM, and DSC techniques. The investigations indicate that all components are homogenously dispersed. Films containing 3% of nano‐Dy₂O₃ are more homogenous and less crystalline, and the same is supported by DSC studies indicating the friendly nature to ionic conductivity. Transference number studies reveal that the major charge carriers are ions. With the increase in % of nano‐Dy₂O₃, the conductivity increases and reaches maximum in 3% film with a value of 1.06 × 10⁻⁴ S/cm (at 303 K). Further, the conductivity of the film increases with raise in temperature due to the hopping of interchain and intrachain ion movements and fall in microscopic viscosity at the matrix interface of the film. Electrochemical cells are fabricated using these films with the configuration “anode (Mg + MgSO4)/[PVA (90%) + Na₃C₆H₅O₇ (10%) + (1–4% nano‐Dy₂O₃)]/cathode (I₂ + C + electrolyte),” and various discharge characteristics are evaluated. With 3% nano‐Dy₂O₃ film, the maximum discharge time of 118 hrs with open‐circuit voltage of 2.68 V, power density of 0.91 W/kg, and energy density of 107.5 Wh/kg are observed. These findings reflect the successful adoption of the developed polymer electrolyte films in electrochemical cells.