Role of Ceria in the Design of Composite Materials for Elemental Mercury Removal

Nanostructured Ceria: Biomolecular Templates and (Bio)applications

Ceria (CeO2) nanostructures are well-known in catalysis for energy and environmental preservation and remediation. Recently, they have also been gaining momentum for biological applications in virtue of their unique redox properties that make them antioxidant or pro-oxidant, depending on the experimental conditions and ceria nanomorphology. In particular, interest has grown in the use of biotemplates to exert control over ceria morphology and reactivity. However, only a handful of reports exist on the use of specific biomolecules to template ceria nucleation and growth into defined nanostructures. This review focusses on the latest advancements in the area of biomolecular templates for ceria nanostructures and existing opportunities for their (bio)applications.

Mercury-bearing wastes: Sources, policies and treatment technologies for mercury recovery and safe disposal

Due to the lenient environmental policies in developing economies, mercury-containing wastes are partly produced as a result of the employment of mercury in manufacturing and consumer products. Worldwide, the presence of mercury as an impurity in several industrial processes leads to significant amounts of contaminated waste. The Minamata Convention on Mercury dictates that mercury-containing wastes should be handled in an environmentally sound way according to the Basel Convention Technical Guidelines. Nevertheless, the management policies differ a great deal from one country to another because only a few deploy or can afford to deploy the required technology and facilities. In general, elemental mercury and mercury-bearing wastes should be stabilized and solidified before they are disposed of or permanently stored in specially engineered landfills and facilities, respectively. Prior to physicochemical treatment and depending on mercury's concentration, the contaminated waste may be thermally or chemically processed to reduce mercury's content to an acceptable level. The suitability of the treated waste for final disposal is then assessed by the application of standard leaching tests whose capacity to evaluate its long-term behavior is rather questionable. This review critically discusses the main methods employed for the recovery of mercury and the treatment of contaminated waste by analyzing representative examples from the industry. Furthermore, it gives a complete overview of all relevant issues by presenting the sources of mercury-bearing wastes, explaining the problems associated with the operation of conventional discharging facilities and providing an insight of the disposal policies adopted in selected geographical regions.

CeO2-Decorated ?-MnO2 Nanotubes: A Highly Efficient and Regenerable Sorbent for Elemental Mercury Removal from Natural Gas

CeO₂ nanoparticle-decorated ?-MnO₂ nanotubes (NTs) were prepared and tested for elemental mercury (Hg⁰) vapor removal in simulated natural gas mixtures at ambient conditions. The composition which had the largest surface area and a relative Ce/Mn atomic weight ratio of around 35% exhibited a maximum Hg⁰ uptake capacity exceeding 20 mg?g^?1 (2 wt %), as determined from measurements of mercury breakthrough which corresponded to 99.5% Hg⁰ removal efficiency over 96 h of exposure. This represents a significant improvement in the activity of pure metal oxides. Most importantly, the composite nanosorbent was repeatedly regenerated at 350 ?C and retained the 0.5% Hg⁰ breakthrough threshold. It was projected to be able to sustain 20 regeneration cycles, with the presence of acid gases, CO₂, and H₂S, not affecting its performance. This result is particularly important, considering that pure CeO₂ manifests rather poor activity for Hg⁰ removal at ambient conditions, and hence, a synergistic effect in the composite nanomaterial was observed. This possibly results from the addition of facile oxygen vacancy formation at ?-MnO₂ NTs and the increased amount of surface-adsorbed oxygen species.

Co3O4/g-C3N4 Hybrids for Gas-Phase Hg0 Removal at Low Temperature

The Co3O4/g-C3N4 hybrids are constructed via the incipient wetness impregnation method by depositing Co3O4 onto the exterior of g-C3N4, and then employed for Hg0 capture within 60–240 °C. The results show that the Co3O4/g-C3N4 hybrid with a Co3O4 content of 12 wt% performs optimally with the highest Hg0 removal efficiency of ~100% at or above 120 °C. The high performances of the Co3O4/g-C3N4 hybrids are probably attributed to the tight interfacial contact between Co3O4 and g-C3N4, with its improved electron transfer, inferring that cobalt oxide and g-C3N4 display a cooperative effect towards Hg0 removal. NO and SO2 shows a significant suppressive influence on the mercury capture performance, plausibly owing to the competing adsorption and side reactions.