Waqas Qamar Zaman

An efficient catalytic degradation of trichloroethene in a percarbonate system catalyzed by ultra-fine heterogeneous zeolite supported zero valent iron-nickel bimetallic composite

Zeolite supported nano iron-nickel bimetallic composite (Z-nZVI-Ni) was prepared using a liquid-phase reduction process. The corresponding surface morphologies and physico-chemical properties of the Z-nZVI-Ni composite were determined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Energy dispersive X-ray spectra (EDS), Brunauer Emmett Teller (BET) adsorption, wide angle X-ray diffractometry (WA-XRD), and Fourier transform infrared spectroscopy (FTIR). The results indicated high dispersion of iron and nickel nano particles on the zeolite sheet with an enhanced surface area. Complete destruction of trichloroethene (TCE) and efficient removal of total organic carbon (TOC) were observed by using Z-nZVI-Ni as a heterogeneous catalyst for a Fenton-like oxidation process employing sodium percarbonate (SPC) as an oxidant. The electron spin resonance (ESR) of Z-nZVI-Ni verified the generation and intensity of hydroxyl radicals (OH•). The quantification of OH• elucidated by using p-chlorobenzoic acid, a probe indicator, confirmed the higher intensity of OH•. The transformation products were identified using GC-MS. The slow iron and nickel leaching offered higher stability and better catalytic activity of Z-nZVI-Ni, demonstrating its prospective long term applications in groundwater for TCE degradation.

Highly active and stable synergistic Ir–IrO2 electro-catalyst for oxygen evolution reaction

ABSTRACT The design of efficient and stable electrocatalysts is still crucial to realize oxygen evolution reaction (OER) in acid and corrosive environment. Inspired by the metal/metal oxides catalysts, we hydrothermally synthesized Ir–IrO2 composites duly confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive spectrometer (EDS), X-ray absorption data, and transmission electron microscope results. A low onset over-potential of merely 234 mV and a Tafel slope of 53 mV dec−1 were obtained for the prepared catalyst Ir–IrO2_0.5AF. In addition, Ir–IrO2_0.5AF catalyst retained high activity for long time under constant potential polarization. The enhanced performance is attributed to the introduction of lower valence Ir as hydrogen acceptor: hydrogen transfers from –OOH intermediate in OER to adjacent H acceptor site, forming intermediate with relatively lower Gibbs free energy, and resulting in higher activity. The present study emphasizes on important role of the lower valence composition in launching H acceptors and providing wide opportunities toward rational designing of efficient and stable electro-catalysts.

Optimized biosynthesis of xanthan via effective valorization of orange peels using response surface methodology: A kinetic model approach

Herein, an enhanced green production of xanthan gum has been achieved by utilizing orange peels. Response surface methodology and kinetic modeling were adapted for the process optimization and its influence on scale up production respectively. Optimal conditions for the maximum xanthan production were 1.62% acid hydrolysis, 85% carbon source of orange peel hydrolysate and 30.4°C temperature. Furthermore, the optimized treatment was conducted in the batch culture fermentor to observe the associated variations during scale up process. In bio-fermentor, to the first time ever, xanthan production along with reducing sugar conversion and utilization rates reached 30.19g/L, 69.29% and 99.99%, respectively. Employed characterization techniques of FTIR, XRD and HPLC confirmed the fermented product as xanthan gum and obtained an average molecular weight of 1.01×106g/mol. This work on account of optimized process parameters presented maximum xanthan production from a waste material.

Rational Manipulation of IrO2 Lattice Strain on α-MnO2 Nanorods as a Highly Efficient Water Splitting Catalyst

Developing more efficient and stable oxygen evolution reaction (OER) catalysts is critical for future energy conversion and storage technologies. We demonstrate that inducing a lattice strain in IrO2 crystal structure due to interface lattice mismatch enables an enhancement of the OER catalytic activity. The lattice strain is obtained by the direct growth of IrO2 nanoparticles on a specially exposed surface of α-MnO2 nanorods via a simple two-step hydrothermal synthesis. Interestingly, the prepared hydride OER activity increases with a lower IrO2 grown mass, which offers an opportunity to reduce the usage of precious iridium and ultimately obtains a specific mass activity of 3.7 times than that of IrO2 prepared under the same conditions and exhibits equivalent stability. The lattice mismatch in the underlying interface induces the formation of lattice strain in IrO2 rather than the charge transfer between the materials. The lattice strain changes are in good agreement with the order of the OER activity. Our experimental results indicate that using the special exposed surface substrates or tuning the supporting morphology structure can manipulate the catalyst materials lattice strain for the design of more efficient OER catalysts.

Limited Ce doped Ni–Co as a highly efficient catalyst for H2-SCR of NO with good resistance to SO2 and H2O at low temperature

The Ni1−xCexCo1.95Pd0.05O4 catalysts doped with limited Ce were fabricated using a sol–gel method and employed to investigate the SO2-resistance in the selective catalytic reduction of NO by hydrogen (H2-SCR). The results indicated that the inclusion of a limited amount of cerium not only effectively enhanced the catalytic activity of Ni1−xCexCo1.95Pd0.05O4 catalysts but also improved their resistance to SO2. Notably, when the Ce doping was 0.07 at%, the catalyst showed high sulfur resistance and exhibited a broader temperature window of 140–350 °C with a maximum NOX conversion of 98% at 190 °C. Also, addition of 5% H2O into the feed gas slightly decreased the deNOX performance of all catalysts, the NOX conversion nearly recovered to the initial level with H2O withdrawal, and the resistance to H2O also increased gradually in correspondence to the increase in Ce doping. Meanwhile, an increase of GHSV from 4800 to 9600 mL h−1 g−1, the NO/H2 ratios from 1 : 10 to 1 : 1 and the O2 content from 0% to 6%, gradually decreased the removal efficiency of NO. The XPD and XRS analysis depicted fine cubic spinel-type structures and Ce bearing two chemical valence states doped in the spinels. In the H2-TPR and NH3-TPD analysis, the Ce doping resulted in the temperature shift of reductive peaks and weak acid sites to lower temperature and the increase of strong acid sites. These results enhanced the redox property and led to a positive effect on SCR reaction, which were consistent with the SCR activity data.

The impact of surface properties and dominant ions on the effectiveness of G-nZVI heterogeneous catalyst for environmental remediation

The surface properties of nanocomposites are influenced by the existence of inorganic species that may affect its performance for specific catalytic applications. The impact of different ionic species on particular catalytic activity had not been investigated to date. In this study, the surface charge (zeta potential) of graphene-oxide-supported nano zero valent iron (G-nZVI) was tested in definitive cationic (Na+, K+, Ca2+ and Mg2+) and anionic (Br-, Cl-, NO3-, SO42-, and HCO3-) environments. The efficiency of G-nZVI catalyst was inspected by measuring the generation of reactive oxygen species (ROS) for the degradation of 1,1,1-trichloroethane (TCA) in sodium percarbonate (SPC) system. Tests conducted using probe compounds confirmed the generation of OH and O2- radicals in the system. In addition, the experiments performed using scavenging agents certified that O2- were primary radicals responsible for TCA removal, along with prominent contribution from OH radicals. The study confirmed that G-nZVI catalytic capability for TCA degradation is notably affected by various cationic species. The presence of Ni2+ and Cu2+ significantly enhanced (94%), whereas Na+ and K+ had minor effects on TCA removal. Overall, the results indicated that groundwater ionic composition may have low impact on the effectiveness of G-nZVI-catalyzed peroxide TCA treatment.

Enhanced effect of EDDS and hydroxylamine on Fe(II)-catalyzed SPC system for trichloroethylene degradation

This study presents a performance comparison of Fe(II)-catalyzed sodium percarbonate (SPC), Fe(II)-EDDS-catalyzed SPC, and of the innovative hydroxylamine hydrochloride (HA)-Fe(II)-EDDS-catalyzed SPC for the degradation of trichloroethylene (TCE) in water. TCE degradation was greater in the Fe(II)-EDDS-catalyzed SPC system compared to the Fe(II)-catalyzed SPC system, indicating the effectiveness of adding EDDS as an enhancement factor for the removal of TCE. Moreover, TCE degradation was faster in the HA-Fe(II)-EDDS-catalyzed SPC system compared to the Fe(II)-EDDS-catalyzed SPC system, illustrating that HA can play a synergistic role in TCE degradation. Analysis of iron distribution in the three systems demonstrated that EDDS addition maintained iron in soluble form, and that the generation of soluble ferrous from ferric iron was expedited with addition of HA. Studies using nitrobenzene and carbon tetrachloride probes provided insights on the generation of hydroxyl radical (HO•) and superoxide anion radical (O2•−) in the three systems. A gradual increasing contribution of O2•− to TCE removal in Fe(II)-catalyzed SPC, Fe(II)-EDDS-catalyzed SPC, and HA-Fe(II)-EDDS-catalyzed SPC systems was verified through free-radical scavenger tests. Finally, monitoring of Cl− concentrations manifested the complete dechlorination of TCE. A possible mechanism of TCE degradation involving two pathways of HO• oxidation and O2•− reaction was proposed.

Highly Efficient Oxygen Evolution Activity of Ca2IrO4 in an Acidic Environment due to Its Crystal Configuration

We systematically characterized the perovskite-like oxides Ca2IrO4 and CaIrO3 as the oxygen evolution reaction (OER) catalysts. Compared with IrO2, universally accepted as the current state-of-the-art OER catalyst, Ca2IrO4 showed an excellent OER catalytic activity in an acidic environment, whereas CaIrO3 did not. X-ray photoelectron spectroscopy (XPS) spectra showed that the oxidation of iridium in Ca2IrO4 and CaIrO3 was slightly beyond +4. X-ray absorption near-edge structure (XANES) spectra illustrated that the IrO6 octahedral geometric structure in Ca2IrO4 and CaIrO3 showed differences. The IrO6 octahedral is asymmetrically distorted and uniformly compressed in Ca2IrO4 and CaIrO3. Therefore, we propose that the IrO6 octahedral distortion plays an important role in the OER activities.