There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.

Nano‐photocatalytic Materials: Possibilities and Challenges

Rising atmospheric levels of carbon dioxide and the depletion of fossil fuel reserves raise serious concerns about the ensuing effects on the global climate and future energy supply. Utilizing the abundant solar energy to convert CO2 into fuels such as methane or methanol could address both problems simultaneously as well as provide a convenient means of energy storage. In this Review, current approaches for the heterogeneous photocatalytic reduction of CO2 on TiO2 and other metal oxide, oxynitride, sulfide, and phosphide semiconductors are presented. Research in this field is focused primarily on the development of novel nanostructured photocatalytic materials and on the investigation of the mechanism of the process, from light absorption through charge separation and transport to CO2 reduction pathways. The measures used to quantify the efficiency of the process are also discussed in detail.

Photocatalytic reduction of CO2 on TiO2 and other semiconductors.

Global warming and climate change concerns have triggered global efforts to reduce the concentration of atmospheric carbon dioxide (CO2). Carbon dioxide capture and storage (CCS) is considered a crucial strategy for meeting CO2 emission reduction targets. In this paper, various aspects of CCS are reviewed and discussed including the state of the art technologies for CO2 capture, separation, transport, storage, leakage, monitoring, and life cycle analysis. The selection of specific CO2 capture technology heavily depends on the type of CO2 generating plant and fuel used. Among those CO2 separation processes, absorption is the most mature and commonly adopted due to its higher efficiency and lower cost. Pipeline is considered to be the most viable solution for large volume of CO2 transport. Among those geological formations for CO2 storage, enhanced oil recovery is mature and has been practiced for many years but its economical viability for anthropogenic sources needs to be demonstrated. There are growing interests in CO2 storage in saline aquifers due to their enormous potential storage capacity and several projects are in the pipeline for demonstration of its viability. There are multiple hurdles to CCS deployment including the absence of a clear business case for CCS investment and the absence of robust economic incentives to support the additional high capital and operating costs of the whole CCS process.

https://www.elsevier.com/__data/assets/pdf_file/0005/96980/Current-status-carbon-capture.pdf

An overview of current status of carbon dioxide capture and storage technologies

A review on g-C3N4-based photocatalysts

Adsorption of $\mathrm{C}{\mathrm{O}}_{2}$ on a semiconductor surface is a prerequisite for its photocatalytic reduction. Owing to superior photocorrosion resistance, nontoxicity, and suitable band-edge positions, $\mathrm{Ti}{\mathrm{O}}_{2}$ is considered to be the most efficient photocatalyst for facilitating redox reactions. However, due to the absence of adequate understanding of the mechanism of adsorption, the $\mathrm{C}{\mathrm{O}}_{2}$ conversion efficiency on $\mathrm{Ti}{\mathrm{O}}_{2}$ surfaces has not been maximized. While anatase $\mathrm{Ti}{\mathrm{O}}_{2}$ (101) is the most stable facet, the (001) surface is more reactive, and it has been experimentally shown that the stability can be reversed and a larger percentage (up to $\ensuremath{\sim}89%)$ of the (001) facet can be synthesized in the presence fluorine ions. Therefore, through density functional calculations we have investigated the $\mathrm{C}{\mathrm{O}}_{2}$ adsorption on $\mathrm{Ti}{\mathrm{O}}_{2}$ (001) surfaces. We have developed a three-state quantum-mechanical model that explains the mechanism of chemisorption, leading to the formation of a tridentate carbonate complex. The electronic structure analysis reveals that the $\mathrm{C}{\mathrm{O}}_{2}\text{\ensuremath{-}}\mathrm{Ti}{\mathrm{O}}_{2}$ interaction at the surface is uniaxial and long ranged, which gives rise to anisotropy in binding energy (BE). It negates the widely perceived one-to-one correspondence between coverage and BE and infers that the spatial distribution of $\mathrm{C}{\mathrm{O}}_{2}$ primarily determines the BE. A conceptual experiment is devised where the $\mathrm{C}{\mathrm{O}}_{2}$ concentration and flow direction can be controlled to tune the BE within a large window of $\ensuremath{\sim}1.5\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. The experiment also reveals that a maximum of $50%$ coverage can be achieved for chemisorption. In the presence of water, the activated carbonate complex forms a bicarbonate complex by overcoming a potential barrier of $\ensuremath{\sim}0.9\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$.

Quantum-mechanical process of carbonate complex formation and large-scale anisotropy in the adsorption energy of C O 2 on anatase Ti O 2 (001) surface

Adsorption of CO$_2$ on a semiconductor surface is a prerequisite for its photocatalytic reduction. Owing to superior photocorrosion resistance, nontoxicity and suitable band edge positions, TiO$_2$ is considered to be the most efficient photocatalyst for facilitating redox reactions. However, due to the absence of adequate understanding of the mechanism of adsorption, the CO$_2$ conversion efficiency on TiO$_2$ surfaces has not been maximized. While anatase TiO$_2$ (101) is the most stable facet, the (001) surface is more reactive and it has been experimentally shown that the stability can be reversed and a larger percentage (up to ~ 89%) of the (001) facet can be synthesized in the presence fluorine ions. Therefore, through density functional calculations we have investigated the CO$_2$ adsorption on TiO$_2$ (001) surface. We have developed a three-state quantum-mechanical model that explains the mechanism of chemisorption, leading to the formation of a tridentate carbonate complex. The electronic structure analysis reveals that the CO$_2$-TiO$_2$ interaction at the surface is uniaxial and long ranged, which gives rise to anisotropy in binding energy (BE). It negates the widely perceived one-to-one correspondence between coverage and BE and infers that the spatial distribution of CO$_2$ primarily determines the BE. A conceptual experiment is devised where the CO$_2$ concentration and flow direction can be controlled to tune the BE within a large window of ~1.5 eV. The experiment also reveals that a maximum of 50% coverage can be achieved for chemisorption. In the presence of water, the activated carbonate complex forms a bicarbonate complex by overcoming a potential barrier of ~0.9 eV.

Quantum Mechanical Process of Carbonate Complex Formation and Large Scale Anisotropy in the Adsorption Energy of CO$_2$ on Anatase TiO$_2$ (001) Surface

BiFeO3 has been widely investigated in many forms and morphologies because of both multiferroic and photovoltaic properties. However, direct growth of vertically aligned BiFeO3 nanorods on an underlying substrate has remained a challenge. In this work, we report template free growth of vertically aligned BiFeO3 nanorods on Fluorine doped Tin Oxide (FTO) coated glass substrate. This has been achieved by a two-step process, in which FeOOH nanorods are grown by chemical bath deposition and converted into BiFeO3 using Bismuth (Bi) coating by physical vapour deposition (PVD). Both DC sputtering and thermal evaporation are attempted under PVD and the results suggest that Bismuth deposited by DC sputtering leads to well-defined BFO nanorods, which shows superior performance in both multiferroic and photoelectrochemical studies. Piezoelectric force microscopy data shows the signature butterfly loop that confirms piezoelectric behaviour with a d33 value of 8 pmV-1 in the BFO nanorods grown by DC sputtering. Further, the M-H hysteresis curve for the same samples reveals remanent magnetization (Mr) value of 0.54 emu cc-1 and antiferromagnetic nature at room temperature. Finally, a stable photocurrent density of 0.05 mA cm-2 is achieved at 0.8 V vs Ag/AgCl under 1 Sun illumination. This work opens up new avenues for BiFeO3 in applications involving 1D nanostructures.

https://iopscience.iop.org/article/10.1088/1361-6528/ab9132/pdf

Template-free fabrication of BiFeO3 nanorod arrays: multiferroic and photo-electrochemical performances.

This article demonstrates implementation of immersed boundary method in continuous casting simulation involving boundary movement. In this methodology, the immersed boundary method is coupled with the second-order accurate finite difference solution of unsteady three-dimensional heat conduction equation. The moving molten metal front is modelled using the immersed boundary method in a Cartesian mesh framework that provides simplicity in its implementation and reduces the computational time as compared to the adaptive mesh solutions. A parallel programming paradigm using message passing interface has been implemented to obtain enhanced computational efficiency. This study has focused on capturing moving boundary during continuous casting and predicts the temperature distribution and shell thickness under different cooling ambiences and casting function. Good agreements with published data and correlations are obtained through numerical analysis. Mould-region shell thickness agrees well with Chipman–Fonders...

Numerical simulation of continuous casting of steel alloy for different cooling ambiences and casting speeds using immersed boundary method

/pdf/evolving-time-surfaces-in-a-virtual-stirred-tank-2ahheetrzc.pdf

Somnath C. Roy

Papers

Quantum-mechanical process of carbonate complex formation and large-scale anisotropy in the adsorption energy of C O 2 on anatase Ti O 2 (001) surface

Quantum Mechanical Process of Carbonate Complex Formation and Large Scale Anisotropy in the Adsorption Energy of CO$_2$ on Anatase TiO$_2$ (001) Surface

Template-free fabrication of BiFeO3 nanorod arrays: multiferroic and photo-electrochemical performances.

Numerical simulation of continuous casting of steel alloy for different cooling ambiences and casting speeds using immersed boundary method

Evolving time surfaces in a virtual stirred tank