Graphitic carbon nitride (g-C
3
N
4
) has become an important material because of its attractive optoelectronic properties. It has been applied in various fields such as photovoltaics, biosensing, ...and photocatalysis. As an analog of graphene, it has layers which can be transformed into different morphologies including nanosheets, nanotubes, and quantum dots. Pristine g-C
3
N
4
exhibits a low specific surface area and a high rate of recombination of photogenerated charges. Therefore, modification is required in order to improve its properties, for instance, by doping it with other atoms and transforming it into another morphology. In this review, the synthesis, modifications, and applications of g-C
3
N
4
are evaluated. The use of theoretical strategies to understand various properties of g-C
3
N
4
and its composites is highlighted. Moreover, the current status on the application of g-C
3
N
4
is explored. Ultimately, this review will shed more light on the uses and modifications of g-C
3
N
4
for future applications.
In the past few years, dye-sensitized solar cells (DSSCs) have received considerable research attention, as potential alternatives to the commonly used, but expensive, silicon-based solar cells owing ...to the low-cost, facile fabrication procedures, less impact on the environment, capability of working even under low incoming light levels, and flexibility of DSSCs. However, the relatively low power conversion efficiencies (PCEs) and poor long-term operational stability of DSSCs still limit their large-scale and commercial applications. As a consequence, this has prompted tremendous research effort towards the realization of high performance and sustainable devices, through tailoring of the properties of the various DSSC components,
via
approaches such as introducing novel materials and new synthesis techniques. Among these, the application of novel materials, especially carbon-based materials, such as graphene and its derivatives, is more appealing due to their excellent optoelectronic, mechanical, thermal and chemical properties, which give them ample potential to replace or modify the traditional materials that are commonly used in the fabrication of the various DSSC components. In addition, the low-cost, abundance, non-toxicity, large specific surface area, flexibility and superior stability of graphene-based materials have enabled their recent use as photoanodes,
i.e.
, transparent conducting electrodes, semiconducting layers and dye-sensitizers, electrolytes and counter electrodes in DSSCs. Recently, the introduction of graphene-based materials into DSSCs resulted in a pronounced increase in PCE from ∼0.13 to above 12.00%. Thus, employing the recent breakthroughs can further improve the optoelectronic properties of the various DSSC components and, hence, close the gap between DSSCs and their silicon-based counterparts that are currently exhibiting desirable PCEs of above 26%. Therefore, this review focuses on the recent applications of graphene-based materials as photoanodes, electrolytes and counter electrodes, for the possible fabrication of all-carbon-based DSSCs. The limitations, merits and future prospects of graphene-based DSSCs are discussed, so as to improve their photovoltaic performance, sustainability and cost-effectiveness.
Graphene-based materials can produce high performance and sustainable DSSCs, through tuning of their excellent optoelectronic, mechanical, thermal and chemical properties for use as photoanodes, photosensitizers, electrolytes and counter electrodes.
South Africa has the largest occurrence of the human immune deficiency virus (HIV) in the world but has also implemented the largest antiretroviral (ARV) treatment programme. It was therefore of ...interest to determine the presence and concentrations of commonly used antiretroviral drugs (ARVDs) and, also, to determine the capabilities of wastewater treatment plants (WWTPs) for removing ARVDs. To this end, a surrogate standard based LC-MS/MS method was optimized and applied for the detection of thirteen ARVDs used in the treatment and management of HIV/acquired immune deficiency syndrome (HIV/AIDS) in two major and one modular WWTP in the eThekwini Municipality in KwaZulu-Natal, South Africa. The method was validated and the detection limits fell within the range of 2–20 ng L−1. The analytical recoveries for the ARVDs were mainly greater than 50% with acceptable relative standard deviations. The concentration values ranged from <LOD – 53000 ng L−1 (influent), <LOD – 34000 ng L−1 (effluent) in a decentralized wastewater treatment facility (DEWATS); <LOD – 24000 ng L−1 (influent), <LOD – 33000 ng L−1 (effluent) in Northern WWTP and 61–34000 ng L−1 (influent), <LOD – 20000 ng L−1 (effluent) in Phoenix WWTP. Whilst abacavir, lamivudine and zidovudine were almost completely removed from the effluents, atazanavir, efavirenz, lopinavir and nevirapine persisted in the effluents from all three WWTPs. To estimate the ecotoxicological risks associated with the discharge of ARVDs, a countrywide survey focussing on the occurrence of ARVDs in WWTPs, surface and fresh water bodies, and aquatic organisms, is necessary.
Display omitted
•Thirteen HIV-ARV drugs were quantified in influents and effluents of three WWTPs.•Matrix effects were minimised by use of labelled surrogate standards.•HIV-ARVDs were prevalent in WWTPs in eThekwini, South Africa.•WWTPs were effective for the removal of most, but not all, ARVDs.•DEWATS showed promise for peri-urban areas not served by conventional sewer lines.
The concentrations of four organophosphate esters (OPEs) were measured in 50 dust samples from homes (n = 10), offices (n = 9), university computer laboratories (n = 12) and cars (n = 19) in Durban, ...South Africa. The median concentrations Σn=4 OPEs were 22940, 26930, 19565 and 49010 ng g⁻1 in homes, offices, university computer laboratories and cars respectively. OPEs were detected in all samples with the exception of one car and one computer laboratory sample in which TDCIPP was not detected. Significant association of indoor characteristics with OPE concentrations was observed. OPEs positively correlated (r = 0.22, p value = 0.4862) with electronics and correlated (r = 0.522, p value = 0.0675) with foams and furniture in homes. By employing the median concentrations and an average dust intake rate, the exposure doses (ng d−1) were found to be 169 (TCEP), 74 (TCIPP), 162 (TDCIPP) and 55 (TPHP) for adults; 159 (TCEP), 70 (TCIPP), 108 (TDCIPP) and 57 (TPHP) for teenagers; 317 (TCEP), 152 (TCIPP), 334 (TDCIPP) and 94 (TPHP) for toddlers. The predominance and exposure magnitude of OPEs in the South African environment require further investigations to determine cumulative human health effects arising from mixtures of these compounds through multiple exposure routes.
•Organophosphate ester (OPE) concentrations in 50 indoor dust samples were measured.•Results indicate widespread use of OPEs in Durban, South Africa.•Cars contained the highest levels of OPEs.•TDCIPP and TCEP, known carcinogens, contributed majorly to human exposure levels.•This is the first report of OPEs in the indoor environment in South Africa.
Graphitic carbon nitride (g-C
3
N
4
) is a metal-free photoactive material which has gained significant interest in the advancement of electronic and optical devices because of its attractive ...optoelectronic properties, such as tuneable band gap, and suitable chemical and thermal stability. This material has been utilized in a range of applications including photocatalysis, biosensing and photovoltaics. Bulk g-C
3
N
4
(B-g-C
3
N
4
) has been shown to exhibit low photo-efficiency due to its low specific surface area and high rate of recombination of photo-generated charges; thus, there is a need for its exfoliation. Also, the type of exfoliation method utilized is crucial. In this work, two exfoliation methods of g-C
3
N
4
, namely, liquid and thermal etching exfoliation, were investigated. Both methods successfully produced g-C
3
N
4
nanosheets, but those synthesized by liquid exfoliation (CNNS-LE) had a much larger specific surface area of 41.68 m
2
g
−1
than those prepared by thermal exfoliation (CNNS-TE) (14.76 m
2
g
−1
) or the parent B-g-C
3
N
4
(3.22 m
2
g
−1
). The band gap energies of B-g-C
3
N
4
, CNNS-LE and CNNS-TE were found to be 2.71, 2.59 and 1.89 eV, respectively. Graphitic carbon nitride nanosheets prepared by thermal exfoliation (CNNS-TE) were found to be 2.5 times more effective in the photo-degradation of Rhodamine B than B-g-C
3
N
4
and CNNS-LE. This is attributed to the positive effect of their porous structure, which gives rise to effective separation of charges, and their extended light absorption properties. Thus, thermal treatment introduces structural defects and electronic modifications that result in an enhanced photocatalytic performance. Consequently, thermal etching is effective in exfoliation of B-g-C
3
N
4
to form a material suitable for photo-driven applications.
A series of three-dimensional (3D) porous nanocomposites, comprised of partially reduced graphene oxide (pRGO) and CO3 2– containing Mg–Al layered double hydroxide, were synthesized in two steps. In ...the first step, graphene oxide (GO) was fabricated by a modified Hummers’ method, and, subsequently, in the second step layered double hydroxide (LDH) nanosheets were homogeneously grown on the surface of the GO sheets by an in situ crystallization approach, involving a facile coprecipitation technique. The alkaline medium used for the in situ growth of LDH on the GO surface resulted in the partial reduction of GO to pRGO, which was confirmed by XRD. XRD also revealed the successful formation of crystalline LDH nanosheets on the surface of pRGO, whereas FTIR spectroscopy confirmed the presence of different functional groups in the nanocomposites. Nitrogen adsorption–desorption studies of the prepared nanocomposites revealed them as high surface area porous materials. Electron microscopic techniques, like TEM and SEM, confirmed that the architectures of the prepared nanocomposites displayed an interconnected 3D network, where a number of LDH nanosheets were interwoven on the surface of pRGO. The elemental mapping and EDX analysis qualitatively confirmed the presence of all of the expected elements in the fabricated nanocomposites. Because of the unique 3D porous network and the presence of a large number of oxygen-containing functional groups, the prepared nanocomposites proved suitable for the adsorption of Pb2+ ions from aqueous solution with a maximum adsorption capacity of 116.2 mg g–1. Equilibrium was achieved after 180 min on conducting the adsorption experiments at pH 4.5. Desorption experiments established the possibility of recovering the metal ions as well as the regeneration of adsorbents for repeated use.
Display omitted
•g-C3N4 can improve the performance and sustainability of new-generation solar cells.•Tunable band gap and high stability of g-C3N4 permit use in DSSC photoanodes.•Excellent ...photocatalysis promotes the application of g-C3N4 in DSSC counter electrodes.•The broad absorption spectrum of g-C3N4 allows use in active layers of PSCs and OSCs.•Superior optoelectronic properties enable use in ETLs and HTLs of PSCs and OSCs.
The unique optoelectronic properties of carbon-based materials have rendered them with tremendous potential to modify or substitute expensive traditional materials that are primarily used to fabricate new-generation photovoltaic devices. Among the carbon-based materials, graphitic carbon nitride (g-C3N4) is more appealing owing to the low-cost and natural abundance of carbon and nitrogen, facile synthesis procedures, biocompatibility, non-toxicity, lightweight, medium band gap, and good thermal and chemical stability. Most importantly, it is possible to tune the band gap of g-C3N4; and hence, optimize its electronic structure via several approaches, such as morphology engineering, chemical functionalization, elemental doping and preparation of nanocomposites. These modifications have recently prompted significant research interest in using g-C3N4 in new-generation solar cells. The incorporation of g-C3N4 into new-generation solar cell layers has not only produced significant improvements in device performance, but also enhanced device stability. Therefore, recent breakthroughs in g-C3N4-based materials can be harnessed to accelerate the development of highly efficient and sustainable new-generation photovoltaic devices. This, in turn, contributes to closing the gap between new-generation solar cells and commercially available silicon solar cells. Herein, we summarize the state-of-the-art advancements made over the last few years, covering the period from 2016 to 2021, by means of incorporating g-C3N4 into the various components of new-generation solar cells. The critical challenges and future prospects for advancing g-C3N4-based new-generation solar cells towards commercial application are also discussed.
The persistence of trace organic chemicals in treated effluent derived from both centralized wastewater treatment plants (WWTPs) and decentralized wastewater treatment systems (DEWATS) is of concern ...due to their potential impacts on human and ecosystem health. Here, we utilize non-targeted analysis (NTA) with comprehensive two-dimensional gas chromatography coupled with time of flight mass spectrometry (GC × GC/TOF-MS) to conduct an evaluation of the common persistent and removed compounds found in two centralized WWTPs in the USA and South Africa and one DEWATS in South Africa. Overall, removal efficiencies of chemicals were similar between the treatment plants when they were compared according to the number of chemical features detected in the influents and effluents of each treatment plant. However, the DEWATS treatment train, which has longer solids retention and hydraulic residence times than both of the centralized WWTPs and utilizes primarily anaerobic treatment processes, was able to remove 13 additional compounds and showed a greater decrease in normalized peak areas compared to the centralized WWTPs. Of the 111 common compounds tentatively identified in all three influents, 11 compounds were persistent in all replicates, including 5 compounds not previously reported in effluents of WWTPs or water reuse systems. There were no significant differences among the physico-chemical properties of persistent and removed compounds, but significant differences were observed among some of the molecular descriptors. These results have important implications for the treatment of trace organic chemicals in centralized and decentralized WWTPs and the monitoring of new compounds in WWTP effluent.
•Non-targeted analysis (NTA) identified 111 common WWTP influent compounds.•11 of the common influent compounds were persistent in the studied WWTP effluents.•Anaerobic treatment reduced chemical peak areas more than conventional treatment.•NTA revealed 5 new compounds not previously reported in WWTP effluent.•Physico-chemical properties did not differ among persistent and removed compounds.
This review article seeks to provide an overview of allergic contact dermatitis (ACD) as a significant environmental and occupational skin disease, the phases of ACD, its causes from the occupational ...and environmental perspectives, its detection, the effects of ACD with respect to the social, psychological, occupational, and financial perspectives, and its cure and/or prevention. Human skin is very sensitive and as the largest organ in the body, it is highly prone to direct and indirect contact with the substances from its environment. The skin reacts to these substances (xenobiotics) differently depending on the individual’s tolerance level or threshold. Allergic contact dermatitis is a significant environmental and occupational skin disease that should not be ignored in our society because it can affect the quality of life of an affected individual. There are multiple causes of ACD, and these causes of ACD have been discussed from two perspectives: environmental and occupational. The effects of ACD can be psychological, social, financial, and occupational. There is need for more public enlightenment on the effects of ACD as well as a precise understanding that it is not a contagious disease so as to significantly reduce the psychological and social effects of ACD on these patients.
PDF
