M. Tahir Soomro

The suitability of ZnO film-coated glassy carbon electrode for the sensitive detection of 4-nitrophenol in aqueous medium

The performance of a ZnO nanoparticle-based electrochemical sensor, fabricated by different treatments of ZnO on glassy carbon electrode, was evaluated for the determination of 4-nitrophenol (4-NP) in aqueous medium. The sensing performance of ZnO film-coated GCE (ZnO/F/GCE) was compared with a variety of electrodes, which included GCEs modified with ZnO powder, RGO (reduced graphene oxide), and RGO-Nafion® composite. Among the fabricated electrodes, the ZnO film-coated electrode, prepared by dispersing the well-sonicated chloroform suspension of ZnO on the GCE, showed excellent response toward the sensitive detection of 4-NP in aqueous medium, and a significant enhancement in the reduction peak current predicted the suitability of the developed sensor. Square wave voltammetry (SWV) detection mode was applied for the determination of 4-NP. The reproducibility and accuracy of ZnO/F/GCE were evaluated in the linear concentration ranges of 0.035 μM to 1.4 μM and 2.1 μM to 6.3 μM. Appreciably low SWV detection limits of 0.008 μM and 0.02 μM were estimated. Minimal influence was observed from the interfering species, added into the sample solution, on the determination of 4-NP. The performance of the developed electrode was initially optimized for 4-NP samples prepared in-house and finally tested against two real samples collected from municipality wastewater. The recovery of the ZnO/F/GCE varied from 96.8% to 105.7%.

The facile synthesis, characterization and evaluation of photocatalytic activity of bimetallic FeBiO3 in natural sunlight exposure

In an effort to develop sunlight active photocatalysts for environmental remediation, a phase pure bimetallic oxide, FeBiO3, was synthesized by a facile route. The optical, structural and morphological properties of the synthesized FeBiO3 were compared with both the parent oxides i.e. α-Fe2O3 and Bi2O3. The synthesized powder exhibited strong absorption in the visible region with the appearance of a distinct optical absorption edge at 2.15 eV. The PL, Raman and IR spectroscopic investigations of the synthesized powder, in comparison to that of pure oxides, confirmed the formation of pure phase FeBiO3 and revealed the dominant role of Fe3+ ions in controlling the optical properties of the material. The X-ray diffraction analysis (XRD) revealed the hexagonal or rhombohedral geometry with an average crystallite size of 20.2 nm, whereas the X-ray photoelectron spectroscopy (XPS) verified the existence of both Fe and Bi in 3+ oxidation states. The electrochemical evaluation of the synthesized catalysts revealed its excellent stability in the neutral and basic pH in the dark and under illumination however, the catalyst was unstable in the harsh acidic medium (pH = 2). A low resistance to electron transfer and better charge retention ability was witnessed by EIS and chronopotentiometry. The photocatalytic activity of the synthesized catalysts was evaluated in the exposure of complete spectrum and visible region of natural sunlight for the removal of chemically stable substrates such as 2-nitrophenol and 2-chlorophenol. The catalysts showed considerably high activity for the removal of both the substrates in the exposure of natural sunlight, whereas 25% less activity was witnessed in visible region in the same span of time. In addition to degradation, the catalyst also exhibited a substantial activity for mineralization (TOC removal). The catalysts unveiled reproducible activity in the repeated scans. The chemical stability and sustained activity both in the complete spectrum and visible region designate it as a potential candidate for photocatalytic environmental remediation.

The effect of cerium alteration on the photocatalytic performance of WO3 in sunlight exposure for water decontamination

In an effort to enhance the photocatalytic activity of cubic WO3 in sunlight exposure, its surface was modified by impregnating the Ce3+ ions ranging from 1% to 25% with a step of 5% with respect to the weight of WO3. Compared to pure WO3, the optical analysis by diffuse reflectance spectroscopy (DRS) revealed better absorption cross-section and red shift in the band edges for Ce loaded catalysts. The decreased intensity of photoluminescence (PL) emissions and the suppression of the Raman active bands of WO3 verified the recombination quenching ability of Ce surface states. The XRD analysis revealed the existence of Ce3+ states in the lower loadings (≤5%), whereas the majority of Ce4+ states were noticed at higher loadings. The FESEM analysis also verified the formation of individual particles of Ce(III,IV) oxides at the surface of WO3 at higher loadings. The XPS analysis of 10% Ce loaded samples also revealed the presence of mixed oxides of Ce at higher loading. Except for 1% Ce loaded WO3, the estimation of charge–discharge capacity, in comparison to pure WO3, revealed the enhancement in the charge retention ability with the increasing Ce loading. In comparison to pure WO3, the synthesized catalysts exhibited superior activity for the removal of 2-nitrophenol and 2-chlorophenol substrates in natural sunlight exposure. The analysis of the degradation data revealed that in the lower concentration the surface oxygen bonded Ce3+ states serve as electron trapping and transfer centers, whereas with the increasing surface density the synergic composite mechanism is the dominating mode. The exaggerated estimation in the EDX analysis of the samples loaded with 15% and 20% Ce also revealed the major surface coverage by the oxides. The salient feature of the study was the evaluation of the photocatalytic activity with the minimal catalyst loading of 350 mg L−1.

A Simple Electrochemical Approach for Determination and Direct Monitoring of Drug Degradation in Water

The application of electrochemical techniques for the determination of pharmaceutical drugs in water is reported here. The experiment is designed for use in undergraduate chemistry courses. Two most commonly used pharmaceutical drugs e.g., ibuprofen (IBP) and paracetamol (PCM) were investigated for their identification and electrochemical investigations using cyclic votlammetry (CV) and square wave (SQW) voltammetry. The major objective of this communication is to enable students to get familiar and use sophisticated electrochemical techniques. A detailed protocol for the detection of IBP and PCM is presented in this work. The developed protocol was used to study sunlight photocatalytic degradation of IBP and PCM in photocatalytic degradation experiments carried out in the presence of ZnO based photocatalyst. This easy and efficient approach can easily be included in undergraduate chemistry courses.

Synthesis, Electrochemical and Antimicrobial Activity of Colloidal Copper Nanoparticles

The colloidal dispersion of copper nanoparticles (CuNPs), prepared by reducing Cu2+ ions using ascorbic acid, was characterized and used for electrochemical and antimicrobial activity investigations. By depositing CuNPs onto the glassy carbon electrode (GCE) surface the CuNPs/GCE was constructed, which was used to study electrochemical behavior of CuNPs and to carry out direct electrochemical detection of trichloroacetic acid (TCA) and 2-chlorophenol (2-CP) in neutral medium. Excellent electrocatalytic ability of CuNPs, assessed by cyclic voltammetry (CV), for the reduction of TCA and 2-CP was detected. The electrochemical impedance analysis (EIS) of the GCE and CuNPs modified GCE evidenced higher charge transfer activity across the modified electrode surface. The antibacterial activity tests of as-synthesized CuNPs on the selected pathogenic strains of Salmonella group B (7.9±0.912), Klebsiella pneumonia (8.33±1.561), Escherichia Coli (15.65±1.612), Enterococcus faecalis (5.4±0.612), Staphylococcus aureus (12.6±1.531) and yeast Candida albicans (11.4.3±1.512), respectively, were performed. The results indicated that the use of CuNPs can be pursued as an alternative strategy (to antibiotics) for averting infections by controlling bacterial adhesion and bacterial bio-film formation against microbial infections.