Akansha Mehta

Enhanced photocatalytic water splitting by gold carbon dot core shell nanocatalyst under visible/sunlight

Hydrogen production from water using photocatalysts under sunlight still remains a huge challenge. The search for a suitable photocatalyst combines an ability to dissociate water molecules with a band gap that absorbs light in the visible range and also water stability. In this regard, our present study represents a facile method for fabricating carbon quantum dots (CQDs) and Au@CQDs, which are useful for photocatalytic hydrogen generation from water. The optical properties revealed a band gap energy (eV) for CQDs (2.78) and Au@CQDs (2.68); additionally, photoluminescence analysis of CQDs showed maximum emission at 460 nm while also exhibiting a red shift when excited at longer wavelengths. Spherical shaped CQDs, with an average size of 7 nm (d spacing of 0.22 nm), and core shell Au@CQDs, with a shell thickness of 6 nm, were observed by HRTEM analysis. Comparatively, both CQDs (260 μmol) and Au@CQDs (280 μmol) displayed a higher rate of hydrogen production under sunlight irradiation than other carbon materials reported in earlier literature. In photoelectrochemical analysis, current densities associated with Au@CQDs and CQDs photoelectrodes (PEs) were found to be 16 mA cm−2 and 6 mA cm−2, respectively at a very low bias of 0.16 V. Moreover, frequency response analysis (FRA) associated with Randels equivalent circuit showed that polarization/charge transfer resistance for Au@CQDs was very low (2.74 Ohm) over that of CQDs PEs (88.8 Ohm), which was 12.9 kOhm for bare TiO2 PEs. All these observations indicate that both CQDs and Au@CQDs are ample for preventing an electron–hole recombination processes, which ultimately leads to superior photocatalytic water splitting.

Enhanced catalytic and antibacterial activity of nanocasted mesoporous silver monoliths: kinetic and thermodynamic studies

Use of low-cost heterogeneous renewable catalysts are essential for effective removal of chemical contaminants like 4-nitrophenol (4-NP) from water bodies. In the present study, for the first time use of surface enhanced (14 m2/g) nanocasted mesoporous silver monolith (AgM) through impregnation into silica monoliths (prepared by sol–gel method) has been demonstrated for its catalytic and antibacterial activity. Highly efficient catalytic reduction rate (2.43 min−1) of 4-NP to 4- aminophenol (4-AP) has been demonstrated using 0.2 gL−1 of AgM catalyst. Enhancement of reduction rate is also observed with increase in temperature (from 25 to 40 °C). Removal of microbial contamination from drinking water is also a prime concern for water purification. Mesoporous AgM shows effective antimicrobial activity against gram negative (E. coli) and gram positive (B. subtilis) bacteria with IC50 values of 75.86 ± 0.173 and 74.56 ± 0.103 respectively at 24 h of incubation.Graphical AbstractUse of low-cost renewable catalysts is essential for effective removal of a chemical contaminant like 4-nitrophenol (4-NP) from water bodies. Nanocasted mesoporous silver monolith (AgM) synthesized via impregnation into silica monoliths (prepared by sol-gel method) has been demonstrated for its catalytic and antibacterial activity. Mesoporous AgM also showed effective antimicrobial activity against gram negative and gram positive bacteria.

Gold Nanoparticles Grafted Mesoporous Silica: A Highly Efficient and Recyclable Heterogeneous Catalyst for Reduction of 4-Nitrophenol

Synthesis of gold nanoparticles dispersed uniformly on mesoporous silica (mAu/SiO2) by homogeneous deposition–precipitation (HDP) method is used as an effective catalyst for reduction of 4-nitrophenol to 4-aminophenol. Silica provides support and surface area to increase the catalytic activity of gold. X-ray photon spectroscopy revealed binding energy of Au 4f7∕2 (∼84.0eV) and Au 4f5∕2 (∼87.7eV) which support the formation of Au0 on SiO2 surface. Au/SiO2 showed Langmuir type-IV isotherms which are the characteristic features of mesoporous materials furthermore, pore size decreases with incorporation of Au NP’s on SiO2 surface. The enhancement is due to the strong interaction of Au0 with silica support. The catalytic conversion was studied by UV-Visible spectroscopy and high performance liquid chromatography (HPLC) quantification method, which shows conversion of nitro group into amino group. In addition, the catalyst was easily separated and reused. The reusability of the catalyst exhibited better reducti...

A sensitive turn on fluorescent probe for detection of biothiols using MnO2@carbon dots nanocomposites

Presently, the combination of carbon quantum dots (CQDs) and metal oxide nanostructures in one frame are being considered for the sensing of purine compounds. In this work, a combined system of CQDs and MnO2 nanostructures was used for the detection of anticancer drugs, 6-Thioguanine (6-TG) and 6-Mercaptopurine (6-MP). The CQDs were synthesized through microwave synthesizer and the MnO2 nanostructures (nanoflowers and nanosheets) were synthesized using facile hydrothermal technique. The CQDs exhibited excellent fluorescence emission at 420nm when excited at 320nm wavelength. By combining CQDs and MnO2 nanostructures, quenching of fluorescence was observed which was attributed to fluorescence resonance energy transfer (FRET) mechanism, where CQDs act as electron donor and MnO2 act as acceptor. This fluorescence quenching behaviour disappeared on the addition of 6-TG and 6-MP due to the formation of Mn-S bond. The detection limit for 6-TG (0.015μM) and 6-MP (0.014μM) was achieved with the linear range of concentration (0-50μM) using both MnO2 nanoflowers and nanosheets. Moreover, the as-prepared fluorescence-sensing technique was successfully employed for the detection of bio-thiol group in enapril drug. Thus a facile, cost-effective and benign chemistry approach for biomolecule detection was designed.

Effect of Surfactants on the Structure and Adsorption Efficiency of Hydroxyapatite Nanorods

Porous hydroxyapatite (HAp) nanorods using surfactant templating proceeded via microwave irradiation method. Study of BET surface area measurement of the HAp nanorods showed that surface area of HAp nanorods with a mixture of cat-anionic surfactants was higher (56.16 m2/g) than their individual counterpart (for anionic 52.8 m2/g and for cationic 48.8 m2/g) as well as without surfactant (19.07 m2/g) due to higher synergistic effect and low critical aggregation concentration of the mixture. Surfactant-directed synthesis of porous HAp has been explored in literature, but the relation between the pore size distribution, surface area and morphology and choice of surfactant(s) was not fully understood and hence in this work we have explored those parameters. The rod shape morphology and the crystal structure of the synthesized HAp nanomaterial were observed by FESEM, HRTEM, and XRD. Due to the higher surface area, HAp nanorods synthesized from the cat-anionic mixture, act as a better adsorbent for dyes and metal ions. The maximum adsorption of dye (methylene blue) was found to be 833.3 mg/g whereas for heavy metal ions like Pb2+ and Cd2+ were 909 and 714.28 mg/g respectively. The kinetic mechanism, the effects of adsorbate pH, temperature, contact time and adsorbent concentration on the dye and metal ions removal were also explored. The antibacterial property of HAp nanorods after doping with silver was investigated against the gram-negative Escherichia coli and gram-positive Bacillus subtilis bacteria by measuring minimal inhibitory concentration (MIC) method.

Amphiphilic carbon dots derived by cationic surfactant for selective and sensitive detection of metal ions

Carbon Dots (CDs) the kind of recently exposed fluorescent nanomaterials have become increasingly popular in the precedent decade due to their distinctive physical and optical properties. Relating to above recognition for the first time we present the synthesis of CDs by cationic surfactant, Cetylpyridinium Bromide (CPB). Due to good carbon content amphiphilicity, and existence of heteroaromatic π system, CPB reveals three advantageous properties including a good carbon source, stabilizing agent, and contributing fluorophore in the CDs system. The as prepared CDs synthesized by hydrothermal technique reveals excellent fluorescent properties having strong green emission at 525 nm when excited over 470 nm. The FTIR results showed the presence of CC, CO, NH, CH and OH bonds. The presence of hydrophilic groups such as carboxyl and hydroxyl groups present on the surface confer them water solubility. The HRTEM results revealed the size of prepared CDs to be in the range of 7-10 nm. The XPS spectrum confirms the presence of Carbon, Oxygen and Nitrogen, suggesting that the CDs have good purity and very little impurities. Latterly CDs were used for the selective and sensitive detection towards Fe2+ ions. Also the as prepared CDs were utilized for real sample analysis.

Implementation of a logic gate by chemically induced nitrogen and oxygen rich C-dots for the selective detection of fluoride ions

The widespread pollution of fluoride ions in the environment badly affects the ecological system due to their high toxicity, mobility and the difficulty of their degradation. So, there is a need to design an environmentally friendly, highly selective and sensitive probe for their detection. Here, we have used natural ingredients (e.g. mosambi peels (Citrus limetta), L-ascorbic acid and urea) and mild reaction conditions to synthesize oxygen and nitrogen-rich fluorescent C-dots, named as OC-dots and NC-dots, respectively. We have proposed a turn-off/-on strategy for the specific recognition and quantification of F− ions. Initially, based on the fluorescence resonance energy transfer (FRET) mechanism, the selectivities of both types of C-dots were investigated towards ten different cations. Both types of C-dot were found to be selective for only Fe3+. The sensitivity of the OC-dot/NC-dot–Fe3+ system was also evaluated for fluoride ion detection and it was found that the OC-dot–Fe3+ ion mixture was only selective for F− ions. The detection limit of the nanoprobe was found to be 0.01 μM, lower than the fluoride toxicity level defined by the U.S. Environmental Protection Agency (>1.5 ppm). The efficiency of the nanoprobe was compared using inductively coupled plasma atomic emission spectroscopy on real samples. The C-dot sensors were operated as different logic gates at the molecular level. All of the experimental data indicated that this probe is green, economical, quick and selective and can be used for establishing chemical logic gates for the detection of F−.

A comparative study on the effect of different precursors for synthesis and efficient photocatalytic activity of g-C 3 N 4 /TiO 2 /bentonite nanocomposites

Graphitic carbon nitride (g-C3N4) was synthesized from three different precursors such as urea, thiourea and mixture of urea and thiourea containing each in the ratio 1:1. The variation in the thermal decomposition and condensation pathways of precursors led to the formation of g-C3N4 with different morphological and photophysical aspects. These were loaded upon TiO2/bentonite nanocomposite to make it visible active. The g-C3N4 synthesized from urea (UC3) was found to be highly influential sensitizer due to its thin and long nanosheet-like morphology, and the nanocomposite prepared by loading of g-C3N4 on TiO2/bentonite (UC3TB) effectively degraded about 85% of the reactive brilliant red-X3BS (RBR-X3BS) dye under visible light irradiation. The high activity was attributed due to the high surface area and pore volume of the nanocomposite along with effective charge separation.