U. S. Hareesh

Enhanced CO2 absorption kinetics in lithium silicate platelets synthesized by a sol–gel approach

Platelet-shaped lithium orthosilicate particles synthesized by a sol–gel approach employing the precursors lithium nitrate and colloidal silica displayed enhanced absorption kinetics for CO2 compared to the powders prepared by a solid-state reaction process involving Li2CO3 and silica. The sol–gel samples showed a CO2 absorption capacity of 350 mg g−1 at an absorption rate of 22.5 mg g−1 min−1, a value 70% higher than the rate of 13.2 mg g−1 min−1 measured with the solid-state samples under similar conditions. The higher sorption kinetics of CO2 by the sol–gel derived lithium orthosilicate could be attributed to the unique platelet morphology of the particles, which have a very small thickness. A porous carbon mesh coated with the sol–gel based particles exhibited CO2 absorption capacity of 150 mg g−1 at an absorption rate of 37.5 mg g−1 min−1. This supported absorbent also showed stable absorption and desorption performance for the 8 cycles examined in this study. The excellent absorption characteristics of the sol–gel prepared powders, more specifically the coated strips, provide a successful pathway for the commercialisation of these materials.

A facile one pot synthetic approach for C3N4–ZnS composite interfaces as heterojunctions for sunlight-induced multifunctional photocatalytic applications

Herein, we report a facile one pot synthetic protocol for the creation of C3N4–ZnS composite interfaces by the co-pyrolysis of a precursor mix containing zinc nitrate, melamine, and thiourea at 550 °C in air. The organic–inorganic semiconductor heterojunctions thus formed displayed increased absorbance in the longer wavelength region and facilitated broad absorption of visible light compared to pure ZnS, C3N4 and conventionally synthesized hybrid samples. The decreased emission intensity, increased photocurrent generation and decreased fluorescence lifetime revealed reduced exciton recombinations in the co-pyrolysed sample containing C3N4–ZnS heterostructures. The samples displayed sunlight driven photocatalytic reduction of nitrophenol as well as hydrogen generation (4 mmol g−1 h−1) by water splitting.

Co3O4–C3N4 p–n nano-heterojunctions for the simultaneous degradation of a mixture of pollutants under solar irradiation

Environmental remediation employing sunlight-active semiconductor nano-heterostructures provides effective solutions for handling emerging contaminants through a greener approach. Herein, we report the creation of ultrafine dispersions of Co3O4 nanoparticles in a g-C3N4 matrix by a simple one-pot synthetic strategy involving the co-pyrolysis of constituent raw materials. Calcination of a homogeneous mixture of melamine and cobalt nitrate at 550 °C/2 h leads to the formation of Co3O4–C3N4 p–n nano-heterojunctions that displayed extended absorption in the visible wavelength region owing to the synergistic role of Co3O4 particles. Moreover, the surface area values of the composites reached 90 m2 g−1, a tenfold increase from the value of 8 m2 g−1 obtained for the pristine C3N4. The band bending, induced by the p–n nano-heterojunctions, leads to the formation of intimate interfaces having enhanced photophysical properties. The mass normalized photoluminescence spectra of the heterojunctions indicated reduced exciton recombinations that are validated further by the enhanced sunlight-induced photocatalytic degradation of a mixture of methylene blue and tetracycline organic pollutants.

C3N4 anchored ZIF 8 composites: photo-regenerable, high capacity sorbents as adsorptive photocatalysts for the effective removal of tetracycline from water

Materials combining the abilities of adsorption and photocatalysis provide a facile solution for pollutant disposal as secondary remediation processes are avoided. Herein, we report a simple strategy for the development of C3N4 anchored ZIF-8 microcrystals as sheathed architectures for the highly efficient adsorption and sunlight induced photocatalytic degradation of tetracycline from solution. An adsorption capacity as high as 420 mg g−1 of adsorbent was realized for a composition containing 60:40 wt% of C3N4 and ZIF. Subsequently, the adsorbed tetracycline was degraded to over 96% in 1 h of sunlight exposure. The effects of pH and adsorbate concentration are studied and valid adsorption and degradation kinetic models are arrived at. The bifunctional composite thus developed offers a photo-regenerable adsorbent for the effective removal of an emerging hazardous contaminant.

Hydrophobic and Metallophobic Surfaces: Highly Stable Non-wetting Inorganic Surfaces Based on Lanthanum Phosphate Nanorods.

Metal oxides, in general, are known to exhibit significant wettability towards water molecules because of the high feasibility of synergetic hydrogen-bonding interactions possible at the solid-water interface. Here we show that the nano sized phosphates of rare earth materials (Rare Earth Phosphates, REPs), LaPO4 in particular, exhibit without any chemical modification, unique combination of intrinsic properties including remarkable hydrophobicity that could be retained even after exposure to extreme temperatures and harsh hydrothermal conditions. Transparent nanocoatings of LaPO4 as well as mixture of other REPs on glass surfaces are shown to display notable hydrophobicity with water contact angle (WCA) value of 120° while sintered and polished monoliths manifested WCA greater than 105°. Significantly, these materials in the form of coatings and monoliths also exhibit complete non-wettability and inertness towards molten metals like Ag, Zn, and Al well above their melting points. These properties, coupled with their excellent chemical and thermal stability, ease of processing, machinability and their versatile photo-physical and emission properties, render LaPO4 and other REP ceramics utility in diverse applications.

Morphologically and compositionally tuned lithium silicate nanorods as high-performance carbon dioxide sorbents

The effective capturing of carbon dioxide using regenerable high capacity sorbents is a prerequisite for industrial applications aiming at CO2 capture and sequestration. The removal of CO2 directly from chemical reaction environments at high temperature is a less energy intensive method of its separation with the added benefit of improved efficiency in equilibrium limited reactions. However, the separation of CO2 at the typical reaction temperatures of 573–1073 K is a challenging task due to the non-availability of absorbents with kinetics comparable to reaction rates. Moreover their poor durability due to sintering and particle growth on prolonged use at high temperature is also an impediment to their practical application. Herein, we demonstrate the development of an efficient CO2 absorbent material, made of Li4SiO4 nanorods, with ultrafast sorption kinetics as well as remarkable durability. These nanorods enabled easier surface reaction with CO2 due to shorter diffusion pathways for lithium from the bulk to the surface of the rods permitting extremely fast absorption of CO2. Furthermore, the compositional tuning of the materials helped to realize absorbents with extraordinary CO2 absorption rates of 0.72 wt% s−1 at 100% CO2/923 K. The exceptional performance of these absorbents at lower temperatures (573–823 K) as well as lower CO2 pressures (0.15 atm) demonstrates their potential in practical CO2 separation applications.

Role of precursors on the photophysical properties of carbon nitride and its application for antibiotic degradation

In this paper, we provide a comprehensive evaluation of graphitic carbon nitride (C3N4) powders derived from the four different precursors melamine, cyanamide, thiourea, and urea for the photocatalytic degradation of tetracycline (TC) antibiotic under sunlight irradiation. The powders were synthesized by employing the conventional thermal decomposition method. The synthesized powders were examined using different characterization tools for evaluating the photophysical properties. The degradation profile revealed that urea-derived C3N4 showed the highest activity while melamine-derived C3N4 showed the least activity. The TC degradation efficiency of the photocatalyst was found to be influenced more by the surface area values despite extended absorption by melamine in the visible light region. Stability tests on urea-derived C3N4 and others were checked by four runs of TC degradation under sunlight irradiation. The synthesized C3N4 powders also confirmed the dominance of urea-derived powders for cyclic stability.

Effect of precursor particle size distribution on the morphology and low wetting behavior of photocatalytic nanocoatings on glass surfaces

The effect of particle size distribution of coating precursor on the morphology and low wetting character of photocatalytic nanocoatings is investigated in the present work. TiO2–SiO2–Al2O3 nanocomposite coatings containing Al2O3 particles of size in the range 20–200 nm have been prepared on glass substrates by an aqueous sol–gel process. A composite sol of titanium dioxide containing 30 mol% silica comprises the matrix sol to which alumina particles (1–10 mol%) having sizes in the range 20 to 200 nm are introduced as stabilized dispersions and further coated on glass substrates by the dip-coating method followed by annealing of the coatings at 400 °C. A composite coating containing 2 mol% boehmite derived alumina (TS-B-2) has been found to be more photoactive under visible light and was low wetting in nature. The higher photocatalytic activity of the TS-B-2 nanocomposite is attributed to the presence of phase pure anatase with crystallite size of 3.7 nm and high surface area of 315 m2 g−1, while the low wetting character is attributed to the hierarchical morphology resulting in uniform surface roughness. The present study significantly highlights the possibility of designing composite precursors containing desired constituent particle sizes to produce nanocoatings differing in grain sizes, surface roughness and morphology, resulting in increased self-cleaning and low wetting properties.

Visible-light-driven photocatalytic properties of binary MoS2/ZnS heterostructured nanojunctions synthesized via one-step hydrothermal route

Here, we elaborate a facile and novel synthesis of a MoS2/ZnS nanojunction photocatalyst and its photocatalytic activity for the degradation of the organic contaminants malachite green and para-nitro phenol. The binary photocatalyst thus synthesized was characterized through different techniques, such as XRD, SEM, TEM, EDAX, BET, DRS, XPS and PL. The integration of MoS2 onto a ZnS lattice stimulates sulfur vacancies, curtailing the forbidden energy gap and facilitating visible light absorption. The formation of nanojunctions between ZnS and MoS2 benefits the segregation of photogenerated charge carriers through the interfaces, resulting in photodegradation rates nearly ten times faster than that of ZnS particles. The durability and stability of the synthesized photocatalyst were established by recyclability experiments. The MoS2/ZnS nanojunction synthesis is scalable and contributes to the advancement of MoS2-based photocatalysts for the efficient degradation of aqueous organic pollutants.

A hybrid sol–gel approach for novel photoactive and hydrophobic titania coatings on aluminium metal surfaces

Photoactive and hydrophobic titanium dioxide–silica coatings on aluminium metal surfaces have been developed by dip-coating of a mixed sol–gel precursor of titanium isopropoxide (TIP) and methyl trimethoxysilane (MTMS). The coating composition of titania–0.5 wt% silica (T–S0.5), annealed at 400 °C in air, effectively degraded 94% and 86% methylene blue after 3 h irradiation under UV and sunlight respectively. A water contact angle of 137° was measured on coated surfaces.