Shamik Chowdhury

Hydrothermal conversion of urban food waste to chars for removal of textile dyes from contaminated waters

Hydrothermal carbonization of urban food waste was carried out to prepare hydrochars for removal of Acridine Orange and Rhodamine 6G dyes from contaminated water. The chemical composition and microstructure properties of the synthesized hydrochars were investigated in details. Batch adsorption experiments revealed that hydrochars with lower degree of carbonization were more efficient in adsorption of dyes. Operational parameters such as pH and temperature had a strong influence on the dye uptake process. The adsorption equilibrium data showed excellent fit to the Langmuir isotherm. The pseudo-second-order kinetic model provided a better correlation for the experimental kinetic data in comparison to the pseudo-first-order kinetic model. Thermodynamic investigations suggested that dye adsorption onto hydrochars was spontaneous and endothermic. The mechanism of dye removal appears to be associated with physisorption. An artificial neural network (ANN)-based modelling was further carried out to predict the dye adsorption capacity of the hydrochars.

Recent advances and progress in the development of graphene-based adsorbents for CO2 capture

With the current high consumption of fossil fuels and the rapid increase in atmospheric CO2 concentrations, there is a strong need for energy efficient and selective capture of CO2 from fossil-fuelled power plants and other large industrial sources. Among the various adsorbents explored by the scientific community for CO2 removal from flue gases, graphene is receiving increased attention because of its unique molecular structure and many exciting properties such as high mechanical strength, excellent thermal conductivity, good chemical stability, large accessible surface area, and tunable porosity. In addition, the facile surface functionalization of graphene leads to production of innovative graphene-based materials that have the potential to be applied as advanced next-generation CO2 adsorbents. As a consequence, graphene and its derivatives have been the subject of intense experimental investigations and theoretical studies in recent years, probing their unmatched structural versatility for CO2 abatement. This review aims at bringing together the latest developments in the rapidly evolving cross-disciplinary field of graphene-mediated CO2 adsorption and it provides new research directions for making further advances toward practical deployment of graphene-based CO2 adsorbents.

Holey graphene frameworks for highly selective post-combustion carbon capture

Atmospheric CO2 concentrations continue to rise rapidly in response to increased combustion of fossil fuels, contributing to global climate change. In order to mitigate the effects of global warming, development of new materials for cost-effective and energy-efficient CO2 capture is critically important. Graphene-based porous materials are an emerging class of solid adsorbents for selectively removing CO2 from flue gases. Herein, we report a simple and scalable approach to produce three-dimensional holey graphene frameworks with tunable porosity and pore geometry, and demonstrate their application as high-performance CO2 adsorbents. These holey graphene macrostructures exhibit a significantly improved specific surface area and pore volume compared to their pristine counterparts, and can be effectively used in post-combustion CO2 adsorption systems because of their intrinsic hydrophobicity together with good gravimetric storage capacities, rapid removal capabilities, superior cycling stabilities, and moderate initial isosteric heats. In addition, an exceptionally high CO2 over N2 selectivity can be achieved under conditions relevant to capture from the dry exhaust gas stream of a coal burning power plant, suggesting the possibility of recovering highly pure CO2 for long-term sequestration and/or utilization for downstream applications.

Plant derived porous graphene nanosheets for efficient CO2 capture

There is an urgent need for the mitigation of climate change through CO2 reduction technologies. In this work, we demonstrate a novel method for production of porous graphene-like nanosheets (PGLNS) from the lignocellulosic fiber of oil palm empty fruit bunches (EFB) by a thermal graphitization technique for efficient CO2 capture. We used a wide range of microscopic and spectroscopic techniques to provide insights into the morphological and structural characteristics of the synthesized PGLNS (with d-spacing of ∼0.35 nm and pore size of <1 nm) obtained from the EFB biomass. The PGLNS show excellent performance as adsorbents for post-combustion CO2 capture. At 25 °C and 1 bar pressure, the maximum CO2 uptake was 2.43 mmol g−1 which is considerably higher than other competitive CO2 adsorbents, including zeolite, activated carbon and some metal organic frameworks. The selectivity of the PGLNS for CO2 over N2 (SCO2/N2 = 18.7), computed from single component isotherms at conditions pertinent to post-combustion applications, is also much higher than that of most of the previously reported adsorbents. Moreover, the significantly low isosteric heat of adsorption (∼21 kJ mol−1) revealed the possibility of desorbing CO2 and regenerating the PGLNS for their repeated use at a much lower energy penalty.

Three-Dimensional Graphene-Based Macroscopic Assemblies as Super-Absorbents for Oils and Organic Solvents

With frequent oil spill incidents and industrial discharge of organic solvents, the development of highly efficient and environment friendly absorbents with both hydrophobic and oleophilic properties have become a top priority. Attributing to exceptionally large specific surface area, intrinsic hydrophobicity, outstanding electrochemical stability and superior mechanical properties, two-dimensional (2D) graphene holds significant promise as advanced absorbents for oil spill response and restoration. However, just as any other carbon allotrope, graphene as a bulk material tends to form irretrievable agglomerates due to strong π–π interactions between the individual graphene sheets. This leads to incompetent utilization of isolated graphene layers for environmental remediation applications. In order to overcome this restacking issue, the integration of 2D graphene macromolecule sheets into 3D macrostructures, and ultimately into a functional system, has materialized as a progressively critical approach in recent years. Consequentially, a wide array of exotic 3D graphene-based macroscopic assemblies (GMAs), such as aerogels, hydrogels, sponges, foams, etc., have been intensively developed during the past five years. Owing to their well-defined and physically interconnected porous networks, these rationally designed macroscopic graphene architectures can support rapid mass transfer in 3D and provide adequate accessible surfaces for molecular absorption, thereby outspreading their application potential. This chapter aims at collating the current state-of-the-art on the development and application of 3D GMAs for ultrafast and recyclable oils and organic solvents absorption. Furthermore, it distinguishes the fundamental knowledge gaps in the domain, and lays out novel strategic research guidelines, all of which will promote further progress in this rapidly evolving cross-disciplinary field of current global interest.

New insights into the role of nitrogen-bonding configurations in enhancing the photocatalytic activity of nitrogen-doped graphene aerogels

Nitrogen (N)-doped graphene aerogels (GAs) have recently emerged as a promising class of photocatalytic materials for a multitude of environmental applications. Their photocatalytic activity depends strongly on the type of N bonding configurations created in the host lattice, which in turn relies on the choice of nitrogen sources employed as molecular precursors. However, there is still no systematic assessment of the photocatalytic activity of N-doped GAs (NGAs) synthesized using different nitrogen containing precursors. Herein, we developed a series of NGAs using different kinds of amine, such as primary and secondary amines, as nitrogen precursors and rigorously evaluated their photocatalytic activity toward degradation of acridine orange under visible light irradiation. The bonding state of N atoms in the NGAs could indeed be effectively modulated by a judicious selection of an appropriate nitrogen precursor. Primary amines resulted mainly in pyridinic N structures whereas pyrrolic N was predominantly obtained from secondary amines. Irrespective of the source of nitrogen, the photocatalytic efficiency of the NGAs was directly correlated to the concentration of pyrrolic N defects in their constituent graphene building blocks. Further, the photodegradation byproducts did not present any significant antibacterial activity, reflecting the ecofriendly nature of the as-prepared novel photocatalysts.