Self-powered photodetectors can work with low power consumption or even without any supply from external power sources, and they are recognized as one of the developing trends of next-generation optoelectronic devices. As one of the most-known n-type metal oxides applied in electronic devices, ZnO nanostructures and their heterostructures with other appropriate materials have been widely applied in the assembly of self-powered UV photodetectors. In this review, the recent research on different types of ZnO-based self-powered UV photodetectors is outlined. ZnO nanostructures with different dimensionalities adopted in these photodetectors are discussed in detail. The influences of specific effects, such as the piezo-phototronic effect, the pyro-phototronic effect, the photo-gating effect, and even their fusions, on modulating the self-powered photo-response of these photodetectors have also been demonstrated. The applications of these photodetectors in UV sensing, environmental recognition, wearable devices, functional devices, and light communication are displayed. Finally, possible opportunities and directions for the future developments of these photodetectors are proposed.

Self-powered UV photodetectors based on ZnO nanomaterials

Carbon quantum dots (CQDs) and graphene quantum dots (GQDs) are new carbon-based nanomaterials with unique electronic, optical, and physicochemical properties. Both CQDs and GQDs have received attention in different material research fields such as optoelectronics, energy harvesting, chemical sensing, and biosensing. The combination of edge effects and/or zero-dimensional quantum-confined structures make them a promising alternative for applications like LED emitters, photodetectors, solar cells, water splitting, and optoelectronic devices. Despite the great potential for using these materials in energy harvesters, their potential in energy applications has not yet been reviewed thoroughly. In this review, we particularly focused on the role of edge effects and attached functional groups on flexible optoelectronic devices for energy harvesting applications. In addition, we also discussed the underlying challenges and future prospects for CQD/GQD-based devices with respect to their performance, sustainability, durability, and cost-effectiveness to efficiently realize their industrial scale-up.

Current and future perspectives of carbon and graphene quantum dots: From synthesis to strategy for building optoelectronic and energy devices

The rapid increase of CO2 content in the atmosphere has caused serious environmental concern. To effectively alleviate the issue, it is of great significance to use electrocatalytic technology to convert CO2 into high value-added energy materials. In this minireview, we present the recent progress in the development of metal-based electrocatalysts for the electrocatalysis of CO2 to formic acid/formate. Firstly, we briefly study the possible reaction pathways and mechanisms of electrochemical reduction of CO2. Secondly, the emerging development of different types of metal-based electrocatalysts (homogeneous catalysts and heterogeneous catalysts) as high-performance catalysts is reviewed for improving process efficiency and productivity. Based on the insights, we summarize the current challenges and the future research directions of metal-based materials for the electrocatalytic reduction of CO2.

Metal-based electrocatalytic conversion of CO2 to formic acid/formate

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Advanced polymeric/inorganic nanohybrids: An integrated platform for gas sensing applications.

High quantum yield photoluminescent N-doped carbon dots for switch sensing and imaging.

The fabrication of flexible as well as self-powered optoelectronic devices is a growing and challenging area of research Some scientists have reported the fabrication of either flexible or self-powered photodetectors recently However, most of the literature studies fail to report the fabrication of self-powered as well as flexible photodetectors This study reports the fabrication of self-powered, carbon dot (CD)-enhanced, flexible ZnO/graphite heterojunction-based UV detector where cellulose paper has been used as the substrate A detailed study on the crystallinity and the defects of the ZnO nanorods has been done with appropriate characterizations The CD-enhanced ZnO/graphite heterojunction showed Schottky characteristics The Schottky parameters such as the barrier height, ideality factor, and the series resistance have also been calculated using the Cheung-Cheung method The observed values of barrier height, ideality factor, and the series resistance are 074 eV, 374, and 503 kΩ, respectively The transient response at self-powered condition has been demonstrated The response time and the recovery time at self-powered condition have also been calculated with the help of the transient response, and those values are ∼2 and ∼32 s, respectively The responsivity and the specific detectivity of the fabricated UV detector have been calculated as 957 mA/W and 427×108 Jones, respectively, at 330 nm wavelength, which is quite comparable with literature-reported values, considering a self-powered photodetector

Growth of Carbon Dot-Decorated ZnO Nanorods on a Graphite-Coated Paper Substrate to Fabricate a Flexible and Self-Powered Schottky Diode for UV Detection.

In this work, a resistive sensor based on multiwalled carbon nanotube (MWCNT) - poly(diallyldi- methylammonium chloride) solution (PDDA) composite is proposed for highly sensitive carbon monoxide (CO) detection at room temperature The surface of MWCNTs is functionalized with PDDA, and the functionalization is investigated by Fourier transform infrared and Raman spectroscopy The MWCNT-PDDA composite is used as a sensing material with deposited interdigitated electrodes (IDE) of silver (Ag) on glass substrates The resistance of the sensors changes due to charge transfer from CO to the positively charged quaternary ammonium group present on PDDA The developed sensors are able to detect very low concentrations of CO gas ranging from 1 to 20 ppm with high sensitivity and limit of detection (LOD) of 127 ppb The interference of other gases and volatile organic compounds is investigated, and the results are presented The influence of humidity and temperature on the sensors is also explored The stability and repeatability of the sensors are examined, and the sensors are almost stable for 2 months with excellent reproducibility The sensors also follow the Langmuir adsorption/desorption model The sensors have shown excellent potential for rapid CO gas sensing, and it can be used in wearable electronics applications

Highly Sensitive Room Temperature CO Gas Sensor Based on MWCNT-PDDA Composite

A facile synthesis of nontoxic luminescent carbon dots for detection of chromium and iron in real water sample and bio‐imaging

Carbon dots (CDs) are one of the most valuable nanomaterials in the recent world because of their diversity in applications. This work reports the applications of N-doped CDs in photoluminescence (PL) based picric acid (PA) sensing and the synthesis of CD- multi-walled carbon nanotubes (MWCNT) nano-composite for UV-photodetection. The CDs were synthesized from cigarette-tobacco by a single-step microwave-assisted heating technique. The detailed characterizations of the synthesized CDs have been performed as well. These synthesized CDs showed an average particle size of 2.8 ± 1.04 nm with a quantum yield (QY) up to ~9.98%. The calculated detection limit (LOD) for PA-sensing was 32.1 ppb, which is relatively low compared to the reported literature considering a wider linear range of concentration (0.1–50 μM). The sensing mechanism is also discussed in detail. This sensing ability was then successfully tested to detect PA acid in real water samples, which showed a good recovery percentage with a minimal deviation of ± 10%. For the second application, the CDs were attached with (MWCNTs) to synthesize a novel UV- photoresponsive CD-MWCNT nano-composite. The photocurrent-generation and the mechanism of electron transfer through the nano-composite have been discussed with detailed explanations. The transient photo-response of the nano-composite has also been presented. This transient response was used to calculate the rise and decay time of the system, and the observed values are of 0.38 and 0.42 s, respectively. Therefore, the ability of the CDs to be used in different areas of applications has opened up a vast range of scopes for the researchers.

N-doped carbon dot from cigarette-tobacco: Picric acid sensing in real water sample and synthesis of CD-MWCNT nano-composite for UV-photodetection

In this article, we have reported the electrochemical reduction of CO2 in a continuous semi-micro reactor for the synthesis of formic acid (HCOOH). The reactor was fabricated with polydimethylsilox...

Tapas K. Mandal

Papers

Growth of Carbon Dot-Decorated ZnO Nanorods on a Graphite-Coated Paper Substrate to Fabricate a Flexible and Self-Powered Schottky Diode for UV Detection.

Highly Sensitive Room Temperature CO Gas Sensor Based on MWCNT-PDDA Composite

A facile synthesis of nontoxic luminescent carbon dots for detection of chromium and iron in real water sample and bio‐imaging

N-doped carbon dot from cigarette-tobacco: Picric acid sensing in real water sample and synthesis of CD-MWCNT nano-composite for UV-photodetection

Continuous Semi-Micro Reactor Prototype for the Electrochemical Reduction of CO2 into Formic Acid