Degradation of organic pollutants by Ag, Cu and Sn doped waste non-metallic printed circuit boards

Zeolite NaP1 synthesized from municipal solid waste incineration fly ash for photocatalytic degradation of methylene blue

The disposal of hazardous municipal solid waste incineration (MSWI) fly ash is a challenge nowadays. Recently, the re-utilization of MSWI fly ash by converting it to useful zeolite-containing materials has attracted attention. However, the zeolitic products fabricated from MSWI fly ash are usually of low quality and rarely reported to be applied for photocatalysis. In this study, valuable zeolites (e.g., NaP1) are synthesized from MSWI fly ash via a modified microwave-assisted hydrothermal method. The key parameters for the hydrothermal method including temperature, duration, the amount of additive, and water volume, are investigated and optimized. Specifically, increasing the hydrothermal temperature can promote the synthesis of zeolitic materials; a relatively long hydrothermal duration is essential to accomplish the assembly of zeolites; the addition of Na₂SiO₃ can increase the precursor for the fabrication of zeolites; the water volume makes little influence on the crystal style of products. Eventually, the hydrothermal condition of 180 °C, 1 h, 0.5 g Na₂SiO₃, and 10 mL water is suggested based on the energy consumption and the quality of zeolites. The product containing zeolite NaP1 from such a condition is further applied to degrade methylene blue by photocatalysis. The removal rate has reached 96% within 12 h, which dramatically surpasses that of the raw fly ash (38%). Such excellent photocatalytic performance is attributed to the 10-fold increased surface area (24.864 m² g^-1) and active metal elements embedding in the zeolite structures.

E-waste management, treatment options and the impact of heavy metal extraction from e-waste on human health: Scenario in Vietnam and other countries

Ho Chi Minh (HCM) City is the most important urban region of Vietnam, Southeast Asia. In recent times, the quantity of electronic waste (e-waste) has been growing by several thousand tonnes every year. In this research, some of the existing and developing technologies being employed for the recycling of e-waste have been reviewed. Accordingly, the paper has been divided into three sections namely, e-waste treatment technologies in Ho Chi Minh City, the effect of heavy metals on human health and the extraction of metals from e-waste using pyrolysis, hydrometallurgy, bioleaching, mechanical, and air classifier methods, respectively. The extraction of precious metals and heavy metals such as Cd, Cr, Pb, Hg, Cu, Se, and Zn from e-waste can be hazardous to human health. For example, lead causes hazards to the central and peripheral nervous systems, blood system and kidneys; copper causes liver damage; chronic exposure to cadmium ends up causing lung cancer and kidney damage, and mercury can cause brain damage. Thus, this study examines the key findings of many research and review articles published in the field of e-waste management and the health impacts of metal pollution.

E-waste derived silica-alumina for eco-friendly and inexpensive Mg-Al-Ti photocatalyst towards glycerol carbonate (electrolyte) synthesis: Process optimization and LCA

Valorization ofe-waste, i.e. waste printed circuit board (WPCB) through mechano-chemical activation to obtain silica as the catalyst support and alumina as the catalyst precursor for eco-friendly synthesis of inexpensive highly proficient photocatalyst has been explored. The WPCB derived silica-supported layered double oxide photocatalyst (MATLS_W) and its counterpart (MATLS_C) involving commercial silica and alumina precursors were synthesized through the wet-impregnation method under energy-efficient solar simulated quartz halogen lamp (SSQHL) irradiations to improve its photocatalytic properties compared to conventional methods. The prepared MATLS_Wpossessed a significantly low band-gap-energy (1.58 eV) that rendered efficient photocatalysis in the green-synthesis of glycerol carbonate (GC) (an effective electrolyte). The catalytic performance of the optimal MATLS_Wresulted in a superior yield of GC (98.68%) compared to that rendered by MATLS_Ccatalyst (GC yield: 96.56%) at optimal process conditions. Detailed life cycle assessment (LCA) of the entire process (deploying Ecoinvent 3.5 database) dictated conducive environmental impacts concerning 1 kg GC synthesis alongside a scale-up study for 1 MT GC synthesis encompassing silica-alumina extraction from WPCB, MATLS_W preparation, and employment of SSQHL-radiated batch reactor (SSQHLBR) (56.64% less energy consumption than conventional). The overall process deploying the novel MATLS_Win conjunction with the effectual reactor demonstrated superiority over the conventional GC synthesis process through appreciable reductions of environmental impact parameters, namely GWP, FDP, and HTP by 5.78%, 3.60%, and 5.72% respectively. The developed green process for e-waste utilization can procreate an effective waste management protocol towards a cleaner world.

Mechanical activation to enhance the natural floatability of waste printed circuit boards

The metal in the waste printed circuit boards (WPCBs) is an excellent secondary metal resource. WPCBs were ground to dissociate, and impurities in the dissociated product were removed by gradient flotation to recover valuable metals in this study. The effects of crushing methods on size composition and dissociation state of the crushed products were studied. Then the gradient flotation experiment was designed to verify the natural floatability of ground materials. Grinding test shows that impact crushing has greater grinding fineness (-0.074 mm) than shear crushing, which is 42.14% and 26.18% respectively with 5 min grinding. The flotation test results illustrate that the natural floatability of impurities increases with the grinding fineness, that is, the yield of floats increases without flotation reagents. For impact crushing and shear crushing, the floats yields are 38.48% and 31.75% respectively, accompanied by 70.53% and 65.46% impurity removal for ground materials with 5 min grinding. Subsequently, 21.61% and 26.35% of impurities can be further removed with the aid of collector. Finally, the recovery of Cu in concentrate reaches 67.84% and 65.75%, respectively. FT-IR proves that the excellent floatability of particles is caused by the significant hydrophobic group. Mechanical grinding has been proved to have double effects of improving dissociation and natural floatability.

From E-Waste to Nb-Pb Co-Doped and Pd-Loaded TiO2 /BaTiO3 Heterostructure: Highly Efficient Photocatalytic Performance

A new and sustainable process was reported for the in situ synthesis of Nb-Pb co-doped and Pd-loaded TiO₂ /BaTiO₃ nanometer heterostructures from waste multilayer ceramic capacitors through a simple chlorination-leaching route. The particle size of the Nb-Pb co-doped heterostructure and the Pd loading were 20-50 nm and less than 5 nm, respectively. The bandgaps of the prepared samples were in the range 2.81-2.92 eV. The optimal simulated-sunlight photocatalytic H₂ production rate and Rhodamine B degradation rate of the prepared heterostructure could reach 576.8 μmol g^-1  h^-1 and 0.29911 min^-1 , respectively, which were approximately 11.3 and 19.1 times higher than those of commercial TiO₂ , and 5.96 and 8.91 times higher than those of bare TiO₂ /BaTiO₃ . The recycled heterostructure exhibited excellent photostability and reusability. Such superior photocatalytic performance of the sample was attributed to the formation of the heterostructure, the Nb-Pb co-doping, and the Pd loading, which enhanced the visible light absorption and charge separation efficiency. Furthermore, DFT calculations were applied to explore the enhanced mechanism. This study demonstrates a sustainable process for the conversion of e-waste to a high-value-added and highefficiency photocatalyst, which has the advantages of waste utilization, low-cost preparation, and environmental protection.

New approach for the transformation of metallic waste into nanostructured Fe3O4 and SnO2-Fe3O4 heterostructure and their application in treatment of organic pollutant

Appropriate recycling of waste to reusable materials is much sought after in the scientific community to control the incessant rising pollution in environment due to insufficient management of waste materials. To address this issue, efforts were directed to obtain SnO₂-Fe₃O₄ nanocomposites from scrap tin plated steel and the use of these composites for the degradation of organic pollutant. We have demonstrated a novel, efficient and facile hydrometallurgy approach for the extraction of iron from waste tin plated steel containers found in plenty in the common waste generated in society. The extracted iron has further been utilized for the preparation of SnO₂:Fe₃O₄ nanocomposites with different compositions (SnO₂:Fe₃O₄ ratio of 93.2:6.8, 85:15, 58:42 and 40:60) using hydrothermal route. The photocatalytic activities of nanocomposite were determined spectroscopically using Rhodamine-B (RhB) as a model dye. Our results indicate that among all the composites with SnO₂ (85%):Fe₃O₄ (15%) exhibits the best photocatalytic efficiency under UV light whereas the composition of SnO₂ (93.2%):Fe₃O₄ (6.28%) is the most efficient in visible light. The above visible light efficiency was supported by density functional theory (DFT) studies which suggest a small amount of pure Fe is present at the Sn sites in the nanocomposite, leading to the reduction in the band gap of the nanocomposite and resulting in absorption in the visible range. Thus, in the present study, we have shown a process of conversion of waste to nanomaterials and its utilization for treatment of organic pollutants.