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

The Equation of Motion, Impedance, and Equivalent Circuit Model for a Magnetoelastic Resonance Sensor

Investigation of Photo-induced enhancement of sensitivity and electrochemical surface phenomenon of multileg TiO2 nanotubes sensor device towards H2O2

Use of Magnetoelastic Sensors for Quantifying Platelet Aggregation I: Whole Blood and Platelet Rich Plasma

TiO2 nanotube arrays formed by electrochemical anodization of Ti metal foil are crystallized through a solvothermal technique at 200 °C (as compared to conventional annealing at 550 °C), which results in anatase phase with granular morphology. The photo-current measurements reveal a higher current-density under the visible light for solvothermally crystallized samples. The photo-current behavior has been analysed and correlated with defect state characterization using X-ray photo-electron spectroscopy, Photo-luminescence, Electron paramagnetic resonance and Mott-Schottky measurements. These studies indicate an oxygen vacancy related defect state at 1.14 eV below the conduction band. Also, the density of defect states in solvothermally crystallised samples is an order of magnitude higher than that in conventionally annealed samples. Furthermore, the photo-voltaic properties are studied through dye-sensitised solar cells. I–V characteristics of DSSC fabricated with solvothermally crystallised samples show comparable efficiency but higher dye-adsorption with respect to the conventionally annealed samples. Such a comparable efficiency at a lower thermal budget leads to reduced ‘energy pay-back time’ in solar cells fabricated with solvothermally crystallised TiO2 nanotube arrays. Finally, we demonstrate a proof-of-concept design of flexible solar cell based on TiO2 nanotubes grown on Kapton substrate and crystallised through the solvothermal technique.

Modified photo-electrochemical and photo-voltaic properties of solvothermally crystallised TiO 2 nanotube arrays

Two-dimensional (2D) Ti3C2Tx MXene and its heterostructure exhibit promising performances in several applications such as energy storage, optoelectronics, electrocatalysis, water purification, biomedical, etc. Our investigation shows that an etching duration of 24 h is sufficient to remove Al layers from Ti3AlC2 and to obtain a well-separated accordion-like structure. Different lateral size monolayer MXene flakes ranging from 2 μm to 35 nm are obtained by tuning the sonication time from 2 to 8 h. The monolayer nature of the flakes is confirmed by both Atomic Force Microscope (AFM) and Transmission Electron Microscope (TEM). Raman vibrational modes and X-ray photoelectron spectroscopy (XPS) show that the flakes are containing –O, –F, and –OH functional groups. A unique type of absorption spectra is observed that comes from both interband and intraband transition. An in-depth structural, vibrational, and optical property study gives a clear idea to use these flakes for heterostructure formation with other materials for various applications. 

Somnath C. Roy

Papers

The Equation of Motion, Impedance, and Equivalent Circuit Model for a Magnetoelastic Resonance Sensor

Investigation of Photo-induced enhancement of sensitivity and electrochemical surface phenomenon of multileg TiO2 nanotubes sensor device towards H2O2

Use of Magnetoelastic Sensors for Quantifying Platelet Aggregation I: Whole Blood and Platelet Rich Plasma

Modified photo-electrochemical and photo-voltaic properties of solvothermally crystallised TiO 2 nanotube arrays

Optimization of etching and sonication time to prepare monolayer Ti3C2T MXene flakes: A structural, vibrational, and optical spectroscopy study