Environment

Microwave (Anton Paar, Monowave 200) assisted synthesis and characterization of metal oxides

In recent times, microwave-assisted liquid phase routes to synthesize inorganic nanomaterials have received much attention due to several advantages compared to conventional heating, including energy efficiency, higher yield, fewer byproducts, short reaction times, improved reproducibility, and remarkable control of reaction parameters. It is theoretically possible to combine microwave irradiation with any liquid-phase synthesis technique. Consequently, the idea provides exciting opportunities as well as unique challenges for the synthesis of inorganic nanomaterials. Domestic microwave ovens are considered inferior to dedicated microwave equipment in terms of safety and parameter control.

In light of these aspects, a dedicated single-mode sealed-vessel microwave reactor is being used to obtain various metal oxides. These nano-sized metal oxides find applications in almost every field of current science and technology, in various ways and forms. The areas of applications include catalysis, energy generation and storage, environmental remediation, electronics, sensors, pharmaceutical preparations, health care, biotechnology, food technology, and other industrial applications.

Solid Sorbents for CO₂ Capture

Carbon dioxide capture and storage (CCS) is a mid-term commercially viable technological option to reduce anthropogenic GHG emissions and best applied to large point sources including fossil fuel power plants, fuel processing plants, and industrial plants (iron and steel, cement, and petrochemicals). CO₂ capture, its transportation, and storage are three main steps in CCS technology. Among these, CO₂ capture is very expensive and, hence, considered the most critical one. CO₂ can be captured using different techniques, including absorption, membranes, cryogenic distillation systems, and adsorption. In recent years, CO₂ adsorption onto solid sorbents has been widely investigated as a means of an alternative to benchmark absorption technology. The selection of a suitable CO₂ adsorbent is a daunting task as the CO₂ needs to be captured from large point sources under different conditions of operation and feed-gas composition. Evidently, each capture scenario presents unique requirements and constraints. An extensive review of literature reveals that numerous classes of solid sorbents have been explored for effective CO₂ capture. However, each of these classes of solid sorbents presents its own advantageous characteristics and intrinsic limitations, providing scope for further research.

The main objective of the work at the environment lab is to investigate CO₂ adsorption on different types of solid sorbents that have been synthesized, with different schemes, for property enhancement. Using a laboratory scale single-column fixed-bed adsorption unit, CO₂ capture properties of different types of solid sorbents were investigated, including; (i) layered double hydroxide derived mixed oxides (LDHs), (ii) carbon-based sorbents from waste biomass resources, and (iii) titania-based adsorbent.

In order to enhance CO₂ capture properties of LDHs, strategies such as K₂CO₃ impregnation, carbon based support, and development of composite were explored. It was found that the addition of support material increased the surface area of neat Mg-Al LDH, leading to enhanced sorption capacity. Alkali metal carbonate impregnation on CGM-supported Mg-Al LDH generated high basic site density due to increased defects concentration, resulting in further enhancement of sorption capacity. Figure 1 shows the TEM micrographs of selected samples.

TEM Micrographs of various LDH samples

Carbonaceous material obtained from Mesuaferrea L. seed cake using HTC technique were also explored for CO₂ capture. Seeds of the Mesuaferrea L. tree, containing 60 – 63% extractable oil, were found to be promising precursors for non-edible oil based biodiesel production. Seed cake is the by-product of biodiesel production and is a waste being disposed. The utilization of such seed cakes for synthesis of valuable carbon materials is always advantageous over other biomass based precursors in many aspects. Manufacture of value-added products, using low-value byproducts of biodiesel production, will definitely help in the commercialization of biodiesel. Additionally, these plants have to be grown only once which, later on, provides continuous support for carbon sequestration by afforestation and reforestation. Carbon sequestration by forests is considered a promising near-term mitigation option for anthropogenic greenhouse gas (GHG) emission. Thus, the development of CO₂ adsorbent using aforesaid kind of biomass waste provides potential means of addressing current global challenges, namely energy insecurity and climate change through an integrated approach towards sustainable development.