Lyman Continuum Galaxy Candidates in COSMOS

Star-forming galaxies are the sources likely to have reionized the universe. As we cannot observe them directly due to the opacity of the intergalactic medium at z ≳ 5, we study z ∼ 3–5 galaxies as proxies to place observational constraints on cosmic reionization. Using new deep Hubble Space Telescope rest-frame UV F336W and F435W imaging (30 orbits, ∼40 arcmin2, ∼29–30 mag depth at 5σ), we attempt to identify a sample of Lyman continuum galaxies (LCGs). These are individual sources that emit ionizing flux below the Lyman break (<912 Å). This population would allow us to constrain cosmic reionization parameters such as the number density and escape fraction (f esc) of ionizing sources. We compile a comprehensive parent sample that does not rely on the Lyman-break technique for redshifts. We present three new spectroscopic candidates at z ∼ 3.7–4.4 and 32 new photometric candidates. The high-resolution multiband HST imaging and new Keck/Low Resolution Imaging Spectrometer (LRIS) redshifts make these promising spectroscopic LCG candidates. Using both a traditional and a probabilistic approach, we find that the most likely f esc values for the three spectroscopic LCG candidates are >100% and therefore not physical. We are unable to confirm the true nature of these sources with the best available imaging and direct blue Keck/LRIS spectroscopy. More spectra, especially from the new class of 30 m telescopes, will be required to build a statistical sample of LCGs to place firm observational constraints on cosmic reionization.

Phyto-Extract-Mediated Synthesis of Silver Nanoparticles Using Aqueous Extract of Sanvitalia procumbens, and Characterization, Optimization and Photocatalytic Degradation of Azo Dyes Orange G and Direct Blue-15

Green synthesis of silver nanoparticles (AgNPs) employing an aqueous plant extract has emerged as a viable eco-friendly method. The aim of the study was to synthesize AgNPs by using plant extract of Sanvitalia procumbens (creeping zinnia) in which the phytochemicals present in plant extract act as a stabilizing and reducing agent. For the stability of the synthesized AgNPs, different parameters like AgNO3 concentration, volume ratios of AgNO3, temperature, pH, and contact time were studied. Further, AgNPs were characterized by UV–visible spectroscopy, FT-IR (Fourier Transform Infrared Spectroscopy), XRD (X-ray Diffraction), SEM (Scanning Electron Microscopy), and EDX (Energy Dispersive X-ray Spectrometer) analysis. FT-IR analysis showed that the plant extract contained essential functional groups like O–H stretching of carboxylic acid, N–H stretching of secondary amides, and C–N stretching of aromatic amines, and C–O indicates the vibration of alcohol, ester, and carboxylic acid that facilitated in the green synthesis of AgNPs. The crystalline nature of synthesized AgNPs was confirmed by XRD, while the elemental composition of AgNPs was detected by energy dispersive X-ray analysis (EDX). SEM studies showed the mean particle diameter of silver nanoparticles. The synthesized AgNPs were used for photocatalytic degradation of Orange G and Direct blue-15 (OG and DB-15), which were analyzed by UV-visible spectroscopy. Maximum degradation percentage of OG and DB-15 azo dyes was observed, without any significant silver leaching, thereby signifying notable photocatalytic properties of AgNPs.

High-Efficiency Wastewater Purification System Based on Coupled Photoelectric–Catalytic Action Provided by Triboelectric Nanogenerator

It is of great importance to explore a creative route to improve the degradation efficiency of organic pollutants in wastewater. Herein, we construct a unique hybrid system by combining self-powered triboelectric nanogenerator (TENG) with carbon dots-TiO2 sheets doped three-dimensional graphene oxide photocatalyst (3DGA@CDs-TNs), which can significantly enhance the degradation efficiency of brilliant green (BG) and direct blue 5B (DB) owing to the powerful interaction of TENG and 3DGA@CDs-TNs photocatalyst. The power output of TENG can be applied for wastewater purification directly, which exhibits a self-powered electrocatalytic technology. Furthermore, the results also verify that TENG can replace conventional electric catalyst to remove pollutants effectively from wastewater without any consumption. Subsequently, the unstable fragments and the plausible removal pathways of the two pollutants are proposed. Our work sheds light on the development of efficient and sustainable TENG/photocatalyst system, opening up new opportunities and possibilities for comprehensive utilization of random energy.

A Recent Study on Remediation of Direct Blue 15 Dye Using Halloysite Nanotubes

A set of lab-scale experiments were designed and conducted to remedy Direct Blue 15 (DB15) dye using nontoxic halloysite nanotubes (HNT) with the view to be utilized in a textile industrial effluent (TIE). The DB15 adsorbed-HNT “sludge” was used as a reinforcing agent and plastic waste to fabricate the composite. To advance the knowledge and further understand the chemical phenomena associated with DB15 adsorption on HNT, different factors like pH value, adsorbate initial concentration, adsorbent dosage, and temperature on the composite were affected experimentally tested. To estimate the adsorption capacity of HNT, nine isotherm models were applied, and it was identified that the Brouers–Sotolongo adsorption isotherm model represented the best accuracy for predicting the adsorption behavior of the HNT. Likewise, the pseudo-second-order reaction was the predominant mechanism for the overall rate of the multi-step dye adsorption process. Additionally, it was demonstrated that the mass transfer during the process is diffusion-controlled, and thermodynamic assessments showed that the process is physisorption.

Organic-free large-pore-sized γ-alumina for the removal of three azo dyes from aqueous solution

A series of γ-alumina with different pore sizes (5.7 nm–21.6 nm) and similar specific surface areas were synthesized via an organic-free method and their adsorption rates and capacities for Congo red (CR), direct blue 78 (DB78) and direct green 26 (DG26) were investigated. The kinetics study reveals that the dye adsorptions of all γ-alumina samples fit the pseudo-2nd-order model. For CR, its k2 and the pore size of absorbent are in a linear relationship at low dye concentrations. Both of the experimental results and Langmuir isotherm calculation results suggest that the dye adsorption capacities of the γ-alumina prepared in our lab are much higher than those of other γ-alumina reported in literatures. GA-1 with the largest specific area of surface and largest size of pores exhibits a CR adsorption capacity up to 4213.6 mg/g. In addition, initial dye adsorption rates of the γ-alumina prepared in-house are much higher than that of the γ-alumina prepared with the commercially available alumina under the same conditions.

Anaerobic Decolorization of Sulfonated Azo Dyes by Sulfate Reducing Bacteria

Aim: The present study was done to find out ability of sulfate reducing bacteria to reduce sulfonated azo dyes found in the textile effluent. Study Design: Isolate Sulfate reducing bacterial strains from dye contaminated soil samples, inoculate and incubate dye supplemented media under static anaerobic condition and measure the decolorization using UV-VIS spectrophotometer. Place and Duration of Study: The samples were collected from Travancore textiles Nemom, Thiruvananthapuram, Kerala, India. Laboratory analysis were performed at Department of Environmental Sciences, University of Kerala, Thiruvananthapuram, India. The study was done for a period of six months. Methodology: The isolated sulfate reducing bacterial (SRB) strains were screened to test the tolerance to selected sulfonated azo dye Direct blue 71. The decolorization assay was done in Postgate media and an aliquot of samples (3mL) were withdrawn periodically, centrifuged at 10,000rpm for 15min. The supernatant was used to assay azo dye reduction by measuring residual absorption at the wavelength 594 nm of the Direct Blue 71. Results were compared with the uninoculated control. The optimization of physicochemical conditions for effective decolorization of the selected bacterial strains was studied at different environmental conditions (pH, temperature, concentration and added co-substrates such as sodium acetate, lactate and mannitol). The biodegradation of sulfonated azo dye was assessed by characterizing the metabolites formed after degradation by Fourier Transform Infrared Spectroscopy (FT-IR). FT-IR analysis revealed only decolorization had occurred without degradation of the dye during the short incubation period of one week. Conclusion: Degradation of azo dyes and other recalcitrant compounds by obligate anaerobes such as sulfate reducing bacteria is a slow process. Hence, extension of incubation period is necessary for the effective and complete degradation of the dye by SRB.