High-efficiency photocatalyst MnFe2O4/g-C3N4 nanocomposites were successfully synthesized to degrade methylene blue (MB). Two types of magnetic recoverable nanocomposite (MG1 and MG2), which were fabricated using co-precipitation and calcination methods, were characterized using various analytical techniques and applied as heterogeneous catalysts for H2O2 activation under simulated sunlight irradiation. The results revealed that composing g-C3N4 in the composites improved the MnFe2O4 crystallinity and increased the material magnetism which facilitated them for efficient recovery using an external magnet. The MG2 synthesis strategy effectively suppressed particle aggregation and immensely increased the active surface area more than for MG1. The quenching experiments revealed that photogenerated electrons played an important role in the catalytic reaction and singlet oxygen (1O2) was a dominant reactive species for MB degradation. The XPS analysis before and after treatment confirmed that the generated 1O2 was derived from the interaction of metal ions and oxygen vacancy in the H2O2 activation. While both nanocomposites exhibited excellent catalytic ability at near-neutral pH levels and for different real water matrices, MG2 had better MB degradation performance but greater difficulty with gravity settling due to its much smaller particle sizes. Therefore, MG2 large-scale production may require more cumbersome steps. However, both nanocomposites showed high crystallinity and very low metal leaching after several uses and still maintained their magnetism. These observations support the use of our MG nanocomposites as potential photocatalysts to activate H2O2 for the degradation of an organic contaminant in water.

Two facile synthesis routes for magnetic recoverable MnFe2O4/g-C3N4 nanocomposites to enhance visible light photo-Fenton activity for methylene blue degradation

Production of ZnO-CoOx-CeO2 nanocomposites and their dye removal performance from wastewater by adsorption-photocatalysis

Abstract Highly ordered pure MCM-41 and In-MCM-41 mesoporous adsorbents (with Si/In = 95 (IM0.05) and Si/In = 90 (IM0.1)) were synthesized using the hydrothermal-assisted method. The structural, morphological and texture characteristics were investigated by XRD, N 2 adsorption–desorption, SEM-EDX, TEM, diffuse reflectance (DR) and FTIR. The broadening XRD diffraction peaks as well as the shifts to higher and lower 2-theta in IM0.05 and IM0.1, respectively, confirmed the incorporation of indium atoms in the MCM-41 structure. SEM-EXD and TEM images showed that pure MCM-41 and IM0.05 preserve a highly long-range well-ordered hexagonal pore structure, on the other hand, high loading of indium (IM0.1) resulted in partially irregular pore-ordering and morphological defects related to a partial dissolution of MCM-41 structure. The infrared spectra of In-incorporated samples showed a decrease in the transmittance intensity of MCM-41 characteristic peaks with little shifts relative to the pure MCM-41 sample. The potential of pure MCM-41 and In-MCM-41 samples for adsorption of dyes was preliminarily investigated. The removal efficiency of both methylene blue and basic yellow-28 (BY28) was enhanced by the incorporation of indium in the MCM-41. The adsorption equilibrium data of BY28 dye on pure, IM0.05 and IM0.1 samples fitted well with Langmuir adsorption model with adsorption capacity of 123.46, 156.99 and 158.48 mg g −1 respectively. The calculated free adsorption energy obtained from D–R isotherm was found to be 26.7 kJ mol −1 referring to that the adsorption of BY28 on IM0.05 adsorbent is chemical. The adsorption kinetic of BY28 on IM0.05 sample followed the pseudo-second-order model. The adsorption experiments revealed that the prepared samples can be used as effective adsorbents for the removal of dyes in aqueous solutions with good recovery and recyclability. Graphical Abstract 

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Highly ordered pure and indium-incorporated MCM-41 mesoporous adsorbents: synthesis, characterization and evaluation for dye removal

Hydrogels of Acacia gum (AG) were synthesized in the reverse micelle core of sodium bis (2-ethylhexyl) sulfosuccinate (AOT) in gasoline medium. The as synthesized hydrogels were used as template to prepare Silver nanoparticle (AgNPs) in situ via the reduction mechanism of NaBH4. The successful synthesis of bare hydrogels and AgNPs loaded nanocomposite hydrogels (AG–Ag hydrogels) were characterized through Fourier Transform Infrared spectroscopy, Thermal gravimetric analysis, Differential Scanning Calorimetry, Scanning Electron Microscopy, energy dispersive X-ray spectroscopy and Transmission Electron Microscopy, and Atomic Absorption Spectroscopy (AAS). Different feeds of the as fabricated GA-Ag hydrogels were used to catalyze the well-known reactions of 4-nitrophenol (4-NP), 2-nitrophenol (2-NP), and Methyl Orange (MO) reduction in aqueous medium at ambient physical conditions. Remarkably, 1000 mg/L of AG–Ag hydrogels with reduced 4-NP and 2-NP into its counterparts, 4-aminophenol and 2-aminophenol in 24 min and 15 min, respectively at room temperature. Similarly, 1000 mg/L of AG–Ag hydrogels reduced MO completely within 25 min. The aforementioned catalytic reactions followed pseudo first order rate kinetics, and it was found that the value of rate constant (kapp) increased by increasing the catalyst amount which, thereby confirms the high conversion rate of the reactants. 
Schematic illustration of fabrication and catalytic action of AgNPs grown inside the pre-synthesized AG Hydrogel matrices.

Acacia Gum Hydrogels Embedding the In Situ Prepared Silver Nanoparticles; Synthesis, Characterization, and Catalytic Application

Amino acids are the most important part of the human biological system due to their role in living processes. The role of amino acids stretches beyond their traditional role as a building block for proteins, and deficiency of amino acids could lead to decreased immunity, digestive problems, depression, fertility issues, lower mental alertness, slowed growth in children, and many other health issues. The acute detection of amino acids is necessary to determine the human health domain. Here, in this review, we summarize and study the calixarenes as complexes that are of immeasurable value and their utilization for amino acid detection. Key factors such as noncovalent forces, limit of detection, and the supramolecular chemistry of calixarenes with amino acids have been well described. This study presents the most recent efforts made towards the development of potential and highly efficient calixarene-based sensors for the detection of amino acids. 

A versatile enrichment of functionalized calixarene as a facile sensor for amino acids

One-pot synthesis of palladium nanoparticles (PdNPs) has been achieved using calix[4]pyrrole hydrazide (MCPTH) as both reducing as well as capping agent. The synthetic procedure involves the use of environmentally benign water as solvent media. MCPTH-PdNPs have been characterized by using various analytical techniques. Transmission electron microscope analysis visualized the presence of well-dispersed and spherical Pd nanoparticles with an average dimension of 3–4 nm. Powder X-ray diffraction pattern portrayed the presence of face-centered cubic crystal structured PdNPs. A zeta potential value of − 26.2 mV suggests better stability of the nanoparticles. The heterogeneous catalytic activity of MCPTH-PdNPs was studied by probing the reduction of two carcinogenic azo dyes, namely, methylene blue and methyl orange in the presence of sodium borohydride. A remedial pathway for the process of dye degradation is proposed where the catalytic activity of Pd is faciled by the transfer of electrons from MCPTH to the metal centre. The mechanism for dye degradation is further substantiated by Density Functional Theory (DFT) calculations. The results of this work provide not only insight into fabrication of nanoparticles using calixarene platforms but also open new vistas to environmental remediation.

Bharat Makwana

Papers

Calix[4]pyrrole Stabilized PdNPs as an Efficient Heterogeneous Catalyst for Enhanced Degradation of Water-Soluble Carcinogenic Azo Dyes