Fazle Subhan

A colorimetric approach for measuring mercuric ions with high selectivity using label-free gold nanoparticles and thiourea

We report a simple colorimetric assay for Hg2+ measurements using label-free gold nanoparticles (Au NPs, 13.0 ± 1.6 nm) with the aid of thiourea (TU). The addition of TU into Au NPs resulted in aggregation of Au NPs with a red-to-blue color change. While in the presence of Hg2+, it inhibited the aggregation of Au NPs induced by TU, resulting in a reverse color change from blue to purple and finally to wine red. These color variations are dependent on the Hg2+ concentration and can be utilized for the colorimetric sensing of Hg2+. This assay requires only 3 min to reach a naked-eye detection limit of 100 nM, which satisfies the guideline concentration of Hg2+ (250 nM) in industrial water regulated by the EPA. And the concentration of Hg2+ is quantitatively determined using a UV-vis spectrophotometer with a limit of detection (LOD) of 40 nM. The response of the assay caused by Hg2+ (2 μM) was 6.0 to 9.1 times higher than those induced by other metal ions (100 μM), indicating its high specificity towards Hg2+. The assay has been applied for the analysis of Hg2+ in drinking and lake water samples with recoveries in the range of 98.3–120.0%.

Effects of alkali-treated agricultural residues on nitrate removal and N 2 O reduction of denitrification in unsaturated soil

Lignocellulosic agricultural residues were utilized as denitrification carbon substrates to improve the purification capacity of unsaturated soil and alleviate nitrate pollution of groundwater. In this study, corncob and wheat straw were treated by calcium hydroxide to improve biodegradability and enhance denitrification potential. Calcium hydroxide treatment decreased the contents of lignin (i.e., from 16.7 wt% to 15.2 wt% in corncob and from 21.9 wt% to 20.6 wt% in wheat straw), increased potential biodegradable carbon by 4.4-5.3 times, reached complete nitrate removal 7-14 days earlier and decreased N2O/(N2O+N2) ratios by 85-99%. The results provide an insight into the application of alkali-treated agricultural residues as denitrification carbon sources to alleviate nitrate transport to groundwater and reduce potential greenhouse effect.

Synthesis, characterization, thermal degradation and urease inhibitory studies of the new hydrazide based Schiff base ligand 2-(2-hydroxyphenyl)-3-{[(E)-(2-hydroxyphenyl)methylidene]amino}-2,3-dihydroquinazolin-4(1H)-one

Abstract The novel Schiff base ligand 2-(2-hydroxyphenyl)-3-{[(E)-(2-hydroxyphenyl)methylidene]amino}-2,3-dihydroquinazolin-4(1H)-one (H-HHAQ) derived from 2-aminobenzhydrazide was synthesized and characterized by elemental analyses, ES+-MS, 1H and 13C{1H}-NMR, and IR studies. The characterization of the ligand was further confirmed by single crystal analysis. The Schiff base ligand was complexed with metal ions like Co(II), Ni(II), Cu(II) and Zn(II) to obtain the bis-octahedral complexes. The ligand and its metal complexes were also studied for their urease inhibitory activities. All the tested compounds show medium to moderate activities for the enzyme, whereas the copper based complex was found to be much more active against urease with an IC50 = 0.3 ± 0.1 μM±SEM, which is even more potent than the standard thiourea. The IC50 of the cobalt complex was 43.4±1.2 μM±SEM, whereas that of the nickel complex was 294.2±5.0 μM±SEM. The ligand H-HHAQ and the zinc complex were inactive against the tested enzyme.

Preparation and hydrodesulfurization properties of cobalt–molybdenum–phosphorous catalysts for removal of dibenzothiophene

Abstract In this study, a series of cobalt–molybdenum–phosphorous acid (Co–Mo–P) impregnating solutions with various Co/Mo molar ratios (0.2, 0.25, 0.3, 0.35) were synthesized, and desulfurization catalysts were prepared by mixing the solutions with γ-Al2O3 through an incipient-wetness impregnation method. The Co–Mo–P supported γ-Al2O3 catalysts were tested in the hydrodesulfurization of dibenzothiophene (DBT). The catalysts were characterized by N2 adsorption–desorption isotherms, XRD, py-FT-IR, and HRTEM. Nitrogen adsorption measurements revealed that the as-prepared catalysts possess high specific surface area and appropriate pore size. XRD showed that Co species and Mo species were well dispersed on the surface of γ-Al2O3 with the addition of phosphoric acid. Py-FT-IR showed that the catalyst with a Co/Mo molar ratio of 0.25 exhibited more Lewis and Brønsted acid sites. The stacking number and slab length of MoS2 nanoclusters changed with various Co/Mo molar ratios as revealed by HRTEM. Among the tested catalysts, Co–Mo–P supported γ-Al2O3 with Co/Mo molar ratio of 0.25 exhibited higher activity and selectivity of biphenyl than the other catalysts.