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Fluoride contamination in water due to natural and anthropogenic activities has been documented as serious problems worldwide commanding a major threat to the environment. Present study focuses to synthesis bacterial-surfactin ( Bacillus subtilis ) mediated nano-hydroxyapatite (HAp), novel adsorbents for defluoridation. HAp particle size and morphology were controlled by varying temperature of 90–150 °C and pH of 7–11, respectively. The TEM and SEM micrographs reveal that the short-rod particle is observed 20–30 nm at 90 °C and pH 11. The ratio between the length (nm) and width (nm) of nanoparticle are decreased from 4.17 to 1.65 with increasing pH (7–11). The selected area diffraction (SAD) of particles are indicated uniform rod-like monocrystals. The XRD and FTIR observations were indicated the synthesized HAp nanoparticles were well-crystallized with purity phase and high quality. The study reflected that the fluoride removal from contaminated water by HAp was increased significantly (R 2 = 99) with the increasing adsorbent concentration, temperature and time, with two-step adsorption process as the first portion a rapid adsorption occurs during first 90 min after which equilibrium is slowly achieved. The adsorption process is closer to Freundlich isotherm (R 2 > 98) than to Langmuir isotherm (R 2 ≈ 92), indicating HAp as a good adsorbent (n > 3). Above 97% of fluoride removal were noticed at a HAp dose of 0.06 g/10 mL. The adsorption kinetics more fit with pseudo-second-order (R 2 = 99) in compare to pseudo-first-order (R 2 ≈ 91). The slope and intercept of Arrhenius equation indicated the activation/adsorption energy (E a ) of 3.199 kJ/mol and frequency factor (A) of 1.78 1/s. Adsorption thermodynamic parameters (free energy (ΔG 0) and entropy (ΔS > 0)) indicates the spontaneous and endothermic reactions of the adsorption process. Thus, newly synthesized HAp nanoparticles exhibit as a good adsorbent for fluoride removal, theoretically and experimentally being applicable for environmental pollution control.

Cobalt oxide (Co3O4) has received great attention for its use in diverse applications in science and technology. The synthesis Co3O4 by ecofriendly green technological process is the great challenge in present day research.Considering the ecofriendly green technological application, the nano-Co3O4 has been synthesized by microbial induced precipitation (MIP) process in presence of Bacillus pasteurii (OD600; 1.2 × 107cells/mL). The Co3O4 particle was synthesized with different microbial amount (10–30 mL) and Co(NO3)2 (0.01M-1.0 M) by MIP process.The results were exhibited anoptimum yield (production yield 218 mg and conversion yield 61%) of “hybrid bio-Cobalt compound”formation at 0.1 M Cobalt ion and 30 mL of B. pasteurii. The XRD results reflect the formation of Co3O4 from “hybrid bio-Cobalt compound” after calcination at 550 °C. SEM and TEM micrograph of synthesized particle reflects the non-specific shape of particle size range at 10–31 nm. The electrochemical capacitive performance was studied through cyclic voltammetry (CV) and galvanostatic charge–discharge methods with 6.0 M KOH as electrolyte. The synthesized nano-Co3O4 after calcinated at 550 °C, leads to the best specific capacitance of 162.78 F g−1 at 1 mA cm−2constant current density. The energy density and power density of the synthesized were noticed as 4.58 Wh kg−1 and 64.29 W kg−1, respectively, which indicates the MIP synthesized nano-Co3O4 particle is supercapacitor. Thus, MIP process, an ecofriendly green technological process is capable to synthesized the supercapacitor nano-Co3O4 by Bacillus pasteurii and its can be applicable to energy and environment research sector.

The feasibility of using the eco-friendly biodegradable surfactant saponin (a plant-based surfactant) from soapberry and surfactin from Bacillus subtilis (BBK006) for the removal of heavy metals from contaminated industrial soil (6511 mg kg −1 copper, 4955 mg kg −1 lead, and 15 090 mg kg −1 zinc) by foam fractionation and a soil flushing process was evaluated under variation of fundamental factors (surfactant concentration, pH, temperature and time). The results of latter process showed that 1–2% Pb, 16–17% Cu and 21–24% Zn was removed by surfactin after 48 h, whereas the removal of Pb, Cu and Zn was increased from 40% to 47%, 30% to 36% and 16% to 18% in presence of saponin with an increase from 24 to 72 h at room temperature by the soil washing process at pH 4. In the foam fractionation process, the metal removal efficiencies were increased with increases in the saponin concentration (0.075–0.15 g L −1 ) and time (24–72 h), whereas the efficiency was decreased with increasing pH (4–10) and temperature (>40 °C). The removal efficiencies of Pb, Cu and Zn were increased significantly from 57% to 98%, 85% to 95% and 55% to 56% with an increase in the flow rate from 0.2 to 1.0 L min −1 at 0.15 g L −1 saponin (pH 4 and 30 °C). The present investigation indicated that the foam fractionation process is more efficient for the removal of heavy metal from contaminated industrial soil in comparison to the soil washing process. The plant-based eco-friendly biodegradable biosurfactant saponin can be used for environmental cleanup and pollution management.

The use of a biodegradable natural plant-based surfactant extracted from soapberry is proposed for the remediation of Ni, Cr and Mn from industrial soil site in Hai-Pu, Taiwan. Batch experiments were performed under variation of fundamental factors (saponin concentration, pH, and incubation time) for metal remediation. Removal of Ni and Mn were increased with increasing saponin concentration (0.015-0.150 g/L), whereas the removal of Cr was increased upto 0.075 g/L saponin. The Ni, Cr and Mn were removed significantly (p < or = 0.05) at near to the neutral and slightly acidic (pH 5 to 8) conditions. Removal efficiency of Ni (99%) from the soil was found to be greater than that of Cr (73%) or Mn (25%) in the presence of saponin at a concentration of 0.150 g/L at pH 5. The removal percentage increased with incubation time where the removal of Ni was faster than that of Cr and Mn. The result indicates the feasibility of eco-friendly removal of heavy metal (Ni, Cr and Mn) from industrial soil by soil washing process in presence of plant derived saponin.