In this work, lead(II) adsorption on activated carbons, tire-derived activated carbon (TAC), and commercial activated carbon (CAC), in a packed-bed column, was simulated using the Aspen Adsorption® V11 flowsheet simulator. The simulator was used to model the fixed-bed adsorption column and to establish the breakthrough curves by varying the initial concentration of lead(II) ions (500 mg/L, 1000 mg/L, 2000 mg/L, and 3000 mg/L), the bed height (0.2 m, 0.3 m, 0.4 m, 0.5 m, and 0.6 m), and the flow rate (9.88 × 10−4 m3/s, 1.98 × 10−3 m3/s, 2.96 × 10−3 m3/s, 3.95 × 10−3 m3/s, and 4.94 × 10−3 m3/s), at constant temperature and pressure of 25 °C and 3 bar, respectively. At the optimum conditions of 500 mg/L lead(II) concentration, 0.6 m bed height, and 9.88 × 10−4 m3/s flow rate, the breakthrough times were 488 s and 23 s for TAC and CAC, respectively. Under the same conditions, the adsorption capacity obtained at t0.5 was 114.26 mg/g for TAC and 7.72 mg/g for CAC. The simulation results indicate the potential of TAC for the adsorption of lead(II) in comparison to CAC.

Highly reactive OH radicals facilitate advanced oxidation processes (AOPs). AOPs are irreplaceable in environmental remediation including but not limited to pollutant degradation. H2O2 leading to OH radicals in iron based fenton systems are well known and few other oxides of alumina and ceria in non-ferrous fenton systems. Majority of studied catalysts materials are in powder form, which limits the catalysts long term applicability in real systems due to separation and regeneration of the catalyst with required catalytic activity, which is costly. In this present work, we have studied anatase phased titania nanotube arrays (TNA) grown on Ti films prepared by an anodization approach for methyl orange (MO) dye degradation under photocatalytic conditions. Key findings reveal long stability of TNAs over fifty reaction cycles in batch process with higher degree of reproducible performance. Complete removal of MO was achieved after six hours of exposure in AM 1.5 G light (equivalent to 1 sun intensity), where hydrogen peroxide accounted for only 1/200th of the amount of initial dye concentration. This superior performance is ascribed to surface oxygen vacancies and Ti3+ sites promoting regeneration of peroxide in the ongoing reaction medium that is consequently transformed to OH radicals. This is further confirmed by the experiments conducted with formic acid, a known hydroxyl radical scavenger, where the dye degradation was observed to be minimal at a near zero rate even after six hours of reaction time, upon measurements with UV-visible spectroscopy. About 38% of the initial dye was oxidized after 1 h into the reaction under light irradiation in a typical system whereas activity was hugely promoted to over 55% when it was coupled with a Pt wire in an electroless process, without supply of additional power. In conclusion, this TNA based new material is highly regarded as environmentally sustainable, easily reusable, non-toxic and commercially viable candidate for real wastewater treatment plants where the treatment plants are usually large tanks constructed in the open space with access to freely available, energetically rich solar power.

Lanthanum based electrocatalytically active perovskites, LaMO3 (M=Cr, Mn, Fe, Co, Ni), were synthesized using a single step solution combustion synthesis technique. The perovskites showed exceptional performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline medium. Based on the experimental results and literature survey, it is suggested that the exceptional activity of Mn and Co based lanthanum perovskite catalyst could be due to the optimum stabilization of reaction intermediates involved in the rate-determining step (RDS) of ORR/OER. According to crystal field theory (CFT), the d-orbital of transition metals are affected by the octahedral arrangement of six negative charges around it. The d orbital degenerates by splitting into two high energy (eg) and three lower energy orbitals (t2g) while maintaining the same average energy level. The rate-determining step in the ORR/OER reaction that based on the eg orbital filling of B site transition metal cations If the d-electrons are less, the valence state goes up and lowering the eg orbital filling that results in strong adsorption of oxygenated species on the B site (strong B-OH bond). This strong bonding limits the overall reaction rate by the slow desorption of OH and its derivatives during ORR/OER. Similarly, too high eg filling causes weak adsorption of oxygenated species that limits the reaction through the slow adsorption of reactants. Therefore, to enhance the activity of ORR/OER reaction it is required to balance the adsorption and desorption of the reactants and the intermediate respectively. The better way is to optimize the eg orbital filling to be nearly 1 (eg = 1).Based on the experimental results and literature survey, it is suggested that the exceptional activity of Mn and Co based lanthanum perovskite catalyst could be due to the optimum stabilization of reaction intermediates involved in the rate-determining step (RDS) of ORR and OER.