Facile synthesis of ternary Ag/AgBr-Ag(2)CO(3) hybrids with enhanced photocatalytic removal of elemental mercury driven by visible light

Investigation on mercury removal and recovery based on enhanced adsorption by activated coke

This work is to systematically study the mercury-removal behavior of activated coke (AC), regeneration of spent AC by microwave treatment and subsequent recycling of Hg⁰. The powdery (AC) was obtained under coal-fired hot gas conditions in a drop-tube reactor. The adsorption mechanism and capacity of the AC for Hg⁰ removal in a H₂O + SO₂ + O₂ atmosphere were investigated. The regeneration of the AC by microwave heating and recovery of Hg⁰ were studied. The results showed that this AC preparation method can greatly simplify the process, and the AC's large surface area, developed pore structure, and abundant functional groups played a key role in the adsorption of Hg⁰. The adsorption mechanism and the optimum reaction conditions were determined, with a highest average Hg⁰-adsorption efficiency of 91% obtained at 70 °C in 3 h. Desorption of Hg⁰ was also studied, in which the alkaline-functional-group content and pore structure were enhanced, and S was detected by X-ray photoelectron spectroscopy in microwave-regenerated AC, which could improve the Hg⁰ removal efficiency increased to 96% after five adsorption/desorption cycles. The Hg⁰ could subsequently be recovered from the desorbed gas by condensation with an efficiency of 87.4% using ice-water.

Ag2CO3-halloysite nanotubes composite with enhanced removal efficiency for water soluble dyes

The release of water soluble dyes into the environment is an utmost concern in many countries. This paper presents the effects of Ag₂CO₃-halloysite composites on the efficient removal of water soluble dyes. In this study, NaHCO₃ solution was added dropwisely to halloysite nanotubes (HNTs) dispersed in aqueous AgNO₃ to form Ag₂CO₃-HNTs composite. The synthesized Ag₂CO₃-HNTs composite was characterized with Diffused Reflectance Spectroscopy (DRS), X-ray Diffraction (XRD), Thermogravimetric analysis (TGA), Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDX) and Fourier Transform Infra-Red (FT-IR) spectroscopy. The photocatalytic activity and the adsorption capacity of Ag₂CO₃-HNTs on methylene blue and rhodamine b dyes were dependent on pH and the amount of HNTs used in the synthesis. The photodegradation efficiency of Ag₂CO₃ was lower when compared with that of the composite material. This observation is due to the reduction in the electron-hole recombination with the HNTs acting as electron trapping site and the enhanced aqueous dispersity of Ag₂CO₃-HNTs. The enhanced adsorption of water soluble dyes by the Ag₂CO₃-HNTs resulted from the electrostatic attraction of cationic dyes to the surface of the HNTs (negatively charged). The Ag₂CO₃-HNTs therefore removed dye pollutants through a combination of photocatalytic and adsorption processes. The results obtained during the study confirmed the potential application of Ag₂CO₃-HNTs composite in water treatment technologies.

Synthesis of LaFeO3/Ag2CO3 Nanocomposites for Photocatalytic Degradation of Rhodamine B and p-Chlorophenol under Natural Sunlight

Novel LaFeO3/Ag2CO3 nanocomposites are synthesized by co-precipitation method for photocatalytic degradation of Rhodamine B (RhB) and p-chlorophenol under visible light irradiation. Heterostructures between LaFeO3 and Ag2CO3 semiconductors are formed during the synthesis of these nanocomposites. Among the nanocomposites prepared with different ratios of LaFeO3 and Ag2CO3, 1% LaFeO3/Ag2CO3 shows the highest photocatalytic activity for the degradation of RhB. Maximum electron-hole pair decoupling efficiency is observed in 1% LaFeO3/Ag2CO3, which causes the greater activity of the heterostructure. Degradation efficiency of 99.5% for RhB and 59% for p-chlorophenol has been obtained under natural sunlight within 45 min. Interestingly, the stability of Ag2CO3 is improved dramatically after making nanocomposite, and no decomposition of the catalyst was observed even after several photocatalytic cycles. Reactive oxygen species scavenging experiments with p-benzoquinone, isopropyl alcohol, and ammonium oxalate suggest that a major degradation process is caused by holes. Degradation of RhB into small organic moieties is detected using LC-MS technique. Further, the efficient mineralization of the degradation products occurs during the catalytic process.

Insight into elemental mercury (Hg0) removal from flue gas using UV/H2O2 advanced oxidation processes

Elemental mercury (Hg⁰) emitted from coal-fired power plants and municipal solid waste (MSW) incinerators has caused great harm to the environment and human beings. The strong oxidized ^•OH radicals produced by UV/H₂O₂ advanced oxidation processes were studied to investigate the performance of Hg⁰ removal from simulated flue gases. The results showed that when H₂O₂ concentration was 1.0 mol/L and the solution pH value was 4.1, the UV/H₂O₂ system had the highest Hg⁰ removal efficiency. The optimal reaction temperature was approximately 50 °C and Hg⁰ removal was inhibited when the temperature was higher or lower. The yield of ^•OH radicals during UV/H₂O₂ reaction was studied by electron paramagnetic resonance (EPR) analysis. UV radiation was the determining factor to remove Hg⁰ in UV/H₂O₂ system due to ^•OH generation during H₂O₂ decomposition. SO₂ had little influence on Hg⁰ removal whereas NO had an inhibitory effect on Hg⁰ removal. The detailed findings for Hg⁰ removal reactions over UV/H₂O₂ make it an attractive method for mercury control from flue gases.

Controllable fabrication of a novel heterojunction composite: AgBr and Ag@Ag2O co-modified Ag2CO3 with excellent photocatalytic performance towards refractory pollutant degradation

The prepared heterojunction composite showed excellent photocatalytic performance due to its high electron–hole separation efficiency.