A review on TiO2/g-C3N4

Download 1,71 Mb.

bet	11/26
Sana	26.04.2022
Hajmi	1,71 Mb.
	#582641

1 ... 7 8 9 10 11 12 13 14 ... 26

Bog'liq
A review on TiO2

Type of heterojunction	Pollutant	Conc. of catalyst (gL⁻¹)	Conc. of pollutant (mgL⁻¹)	Degradation time (minutes)	Light source	% degradation	No. of times greater than g-C₃N₄	Times greater than TiO₂
Reference
Mesoporous	RhB	2.0	4.79	80	350 W xenon arc lamp (λ > 420 nm)	100	3.1	7.2	[124]
Mesoporous	RhB	1.0	10	180	500 W xenon lamp λ > 400nm	100	2.5	negligible	[118]
Mesoporous	Phenol	0.5	10	60	500 W Hg (Xe) λ < 420 nm	……	8.5	negligible	[212]
Core-Shell	tetracycline	1.0	20	----	300 W xenon lamp	-------	2.3	2	[132]
Core-Shell	Phenol		5	360	500W Xe lamp (λVis ≥ 450 nm	……	7.2	---	[137]
Core-Shell	RhB	1.33	4.79	100	300 W Xe arc lamp λ > 400nm	93.3	1.4	3	[109]
Core-Shell	congo red (CR),	------	--------	120	simulated sunlight	97	1.5	5	[108]
2D-0D	RhB	0.4	10	240	300 W Xe lamp λ > 400nm	98.5	10	40	[213]
2D-0D	Acid Orange 7 (AO7)	1.0	17.5	60	250 W tungsten-halogen lamp λ ∼380-800 nm.	80	2	1.6	[214]
2D-0D	RhB	1.0	10	300	500W Xenon lamp(λ > 420 nm)	84	2.5	3.95	[215]
2D-0D	methylene blue (MB)	1.0	10	360	500W Xenon lamp λ > 420 nm)	-------	3.5	8	159
2D-0D	methyl orange (MO)	1.0	5	180	350W Xenon lamp	80.33	2.80	negligible	[156]
2D-0D	RhB	40mg	10	80	30 W LED light	-------	4.56	3.87	[211]
2D-0D	MO	1.0	10	90	300 W Xe lamp (λ > 420 nm).	80	4	3.2	[216]
2D-0D	RhB	0.8	10	420	24 W visible-light lamp	------	1.8	1.66	[217]
2D-0D	Isoniazid	0.2	50	240	UV light	79.5	3.36	1.1	[168]
2D-1D TGCN heterojunction
TiO₂ nanobelts/g-C₃N₄ nanosheets	MO	1.0	10	120	300 W Xe lamp, λ > 420 nm).	95.1	6.12	9.56	[147]
g-C₃N₄/TiO₂ (NT)	RhB	0.4	5	60	65W CFL lamp	96.7	2.33	negligible	[112]
g-C₃N₄/TiO₂ (NR)	RhB	0.4	5	60	65W CFL lamp	94.5	2.0	negligible	[112]
g-C₃N₄/TiO₂ nanotube	2-chlorophenol	0.5	30	180	Visible light	96.6	--	--	[173]
g-C₃N₄/TiO₂ nanotube	Isoniazid	0.2	50	240	UV light	90.8	4.04	1.18	[168]
2D-2D	RhB	1.0	20	120	300 W Dy lamp λ > 420 nm).	97	1.2	3.2	[218]
2D-2D	Cr (VI)	1.0	10	120	300 W Dy lamp λ > 420 nm	75	1.92	1.15	[218]
2D-2D	MO	0.3	10	15	300 W, Xe arc lamp	98	3.2	2.33	[100]
2D-2D	NO	20 mg	40	60	500 W commercial tungsten halogen lamp	12.6	5.8	---	[219]

3.2.2.2. Kinetics study of photodegradation
According to Ma et al, the photo decomposition of RhB over TGCN follows pseudo-first-order kinetic model as per the Eq. (17) [109].(17)ln C₀/C_t = ktWhere k is the rate constant, C₀ equilibrium adsorption concentration of RhB at dark after 2 h and C_t is concentration of RhB after time t mins under visible light irradiation. The k value of photoccatalytic degradation of RhB by TGCN heterojunction was found to be 0.058 min⁻¹ which was quite higher than that of TiO₂ (0.00056 min⁻¹) and g- C₃N₄ nanosheets (0.017 min⁻¹). The heterojunction showed an enhanced efficiency of 103.6 and 3.4 times greater than that of TiO₂ and g-C₃N₄ nanosheets respectively. The result signified that the heterojunction endowed a conducive path for the exodus of photon induced carriers which boosted the photocatalytic activity [154]. The k value also depended on the amount of g-C₃N₄. The highest k value of TGCN core-shell structure was found to be 2.1 × 10^–2 min^–1for an optimal g-C₃N₄ content of 15 %. The value of k was declined to 1.5 × 10^–2 min^–1 on increasing g-C₃N₄ content to 20 %. This might be attributed to the diminution of magnitudes and quality of effective interfaces formed between g-C₃N₄ shell and TiO₂ core. Moreover, the increase in thickness of g-C₃N₄ shell (20 %) on TiO₂ core led to weaker reflection of light within the interior parts of sphere and hence, utilization of light was decreased [109].
4. Stability of TGCN heterojunction
The practical applicability of a photocatalytic system depends on its stability and reusability. The recycling tests for hydrogen generation and pollutant degradation provide information to assess the stability and recyclability of TGCN heterostructure system [198,230,231]. Li et al have shown that TGCN heterojunction displayed a steady H₂ evolution for five cycles of photocatalytic reaction in 30 h without apparent deactivation, indicating a favourable photo-catalytic stability and excellent reproducibility [197]. Stability of the heterostructure was also confirmed form XRD, FTIR, TEM and SEM studies. Yang et al demonstrated by analysing the XRD pattern [Fig. 9(a)] and TEM image [Fig. 9(b) and (c)] that the crystal structure and morphology of heterojunction were retained after four cycles [154]. Hao and his co-workers confirmed that chemical structures of the heterosturcture photocatalyst would not undergo any change after 4 cycles of photodegradation of RhB as the FT-IR patterns [Fig. 9(d)] of the reused photocatalyst had not changed significantly in comparison to as-prepared one [124]. SEM images [Fig. 9(e) and (f)] revealed that the g-C₃N₄ on the surface of TiO₂ hollow microspheres remained almost unchanged after five cycles suggesting excellent stability and reusability [109]. All such characteristics established that TGCN heterojunction can be a robust photocatalyst with excellent stability and laid the foundation for its industrial application.

Download : Download high-res image (612KB)
Download : Download full-size image

Fig. 9. (a) XRD patterns of TGCN fresh and used (after four cycles) samples, TEM images of (b) fresh, (c) used (after four cycles) TGCN samples (Reproduced from Ref. No. [154]), (d) FTIR spectra of fresh and used (after four cycles) samples of TGCN heterojunctions (Reproduced from Ref. No. [124]), SEM images (e) fresh, (f) used samples (after five cycles) of core-shell TGCN hollow microspheres (Reproduced from Ref. No. [109]).
5. Conclusion and perspectives
TGCN composite can be recognised as a robust, environmentally benign as well as sustainable photocatalyst for generation of renewable H₂ energy and degradation of pollutants to curb unpredictably increasing energy crisis vis-a-vis alarmingly rising environmental pollution. Present review briefly summarised the synthesis principles for construction of TGCN heterostructure with systematically highlighting the limitations underlying in type-II and Z-scheme heterojunction. A comprehensive overview was made on designing strategies and advantages of morphology based TGCN heterojunctions such as mesoporous, core-shell, point-to-face (0D/2D), line-to-face (1D/2D) and face to face (2D/2D) architectures. Combination of TiO₂ with g-C₃N₄ enables the heterojunction to absorb radiation from UV and visible region. Morphology based heterojunctions exhibited enriched light absorption range in the visible region due to the presence of g-C₃N₄, Ti³⁺ and oxygen vacancy. In particular, the band bending at the interface of 2D/2D heterojunction minimises the local band gap energy and widens the absorption range for visible light absorption. Morphology based TGCN heterostructure provides an intimate interfacial contact that enhanced charge transfer ability to suppress recombination of charge carriers for significantly high photocatalytic activity. For instance, photo-generated carriers migrate efficiently through N O Ti covalent heterojunction and the recombination of charge carriers is comprehensibly prohibited. Overall, morphology based TGCN heterostructure can successfully be applied for efficient photocatalytic/ photoelectrochemical H₂ generation and photodegradation of various pollutants by harnessing solar radiation leading to sustainable development. This was pictorially presented in Scheme 4. Despite significant development in photocatalytic performance of morphology based TGCN heterostructure, the efficiency is still less from the expectation, which restricted these photocatalysts from large scale application and commercialisation. Therefore, following efforts should be made to address this challenge.
(i)
Though most of researches have focussed on increasing light absorption range and efficient migration of charge carriers across the interface for enhanced performance, the activity is unsatisfactory because of poor adsorption affinity for pollutants. Ample active adsorption sites on the photocatalyst surface led to substantial contact with the pollutants, which in turn promoted the photocatalytic reaction commendably. The best way to increase the adsorption ability is to conspicuously enhance the surface area which lies far from the expectation. This could be possible by introducing porosity through textural modifications.
(ii)
TGCN heterojunction system exhibited excellent stability and reproducibility up to maximum of five cycles which is needed to be increased. Further, attention should be given for easy and quick recycling without which the technology cannot be implemented for scale up.
(iii)
Although morphology based TGCN heterojunction extends visible-light absorption to longer wavelengths, the absorption range is required to be increased further even up to near infra-red in order to utilize complete solar spectrum.
(iv)
Despite excellent charge separation and migration process occurs through an intimate interfacial contact obtained by means of morphology based TGCN heterojunction, the prime challenge appears before the scientific community to develop a thorough understanding on the mechanism involved in rapid charge transfer process in order to further hasten photocatalytic performance.
(v)
Large number of recent studies has proven that morphology based TGCN heterojunction is a versatile candidate for photocatalytic and photoelectrochemical applications. The exponential growth of this system will undoubtedly continue in future. However, there are enough opportunities and challenges, which will explore further research in improving its photocatalytic /photoelectrochemical performance. Though the present system is extensively investigated for photocatalytic H₂ generation and pollutant degradation, there is ample scope for the future to thoroughly study other aspects of photocatalysis particularly CO₂ reduction. Some important aspects like charge dynamics, optical absorption and electronic band structure are needed to be deeply studied through density functional theory (DFT) computations along with experimental verifications for further improving photocatalytic activity. Photoelectrochemical activity evaluation with respect to H₂ generation and O₂ evolution is required to be deeply studied with the help of TGCN heterojunction. Emphasis must be given by the researchers in future to achieve much higher photocurrent densities.
(vi)
By and large, it is indispensable to transform this lab-scale research in to industrial scale in order to make TGCN heterojunction as a next generation pragmatic photocatalytic system.

Download : Download high-res image (816KB)
Download : Download full-size image

Scheme 4. Visible light driven morphology based TGCN heterojunctions towards sustainable development through efficient photocatalytic/ photoelectrochemical energy generation and environmental remediation.

Download 1,71 Mb.

Do'stlaringiz bilan baham: