Insight into the Role of Size Modulation on Tuning the Band Gap and Photocatalytic Performance of Semiconducting Nitrogen-Doped Graphene

Enhanced removal of dimethyl phthalate using heterogeneous UVC/VUV-Fenton amendment with Fe3O4@CM-β-CD/rGO catalyst: Efficiency, degradation mechanism and toxicity

Dimethyl phthalate (DMP) is widely used as plasticizer, and this kind of plastic industry wastewater is refractory due to the complex chemical structure and endocrine disrupting property. In order to effectively degrade and mineralize DMP contaminated wastewater, a heterogeneous UVC/VUV-Fenton catalyst system was designed with the amendment of targeted design catalyst Fe3O4@CM-β-CD/rGO with core-shell like structure covered with loose convex folded lamellar. The optimum removal and mineralization efficiency of DMP were 98.6 % and 62.8 % in 30 min with 150 mg L-1 Fe3O4@CM-β-CD/rGO and 8 mmol L-1 H2O2. This efficient and fast removal were attributed to a variety of photocatalytic oxidative active species •OH, •O2- and h+ with 59.6%, 29.1% and 9.9% contribution ratio, which mainly took effect on benzene ring open and side-chain fracture by oxidative, hydrolysis and hydrogen substitution determined by the rupture energy requirement from chemical bond in DMP. The target function of CM-β-CD in catalyst controlled the photo-electron generation rate and shorten mass transfer distance by the cladding lamellar, moreover, rGO accelerated the redox between Fe (II) and Fe (III) and electron transfer. The catalytic recovery and removal to DMP kept above 90 % after five recycles. This study provided an excellent performance catalyst and an effective photo-Fenton approach and for the treatment of endocrine disrupting wastewater.

Design, Fabrication, and Mechanism of Nitrogen-Doped Graphene-Based Photocatalyst

Solving energy and environmental problems through solar-driven photocatalysis is an attractive and challenging topic. Hence, various types of photocatalysts have been developed successively to address the demands of photocatalysis. Graphene-based materials have elicited considerable attention since the discovery of graphene. As a derivative of graphene, nitrogen-doped graphene (NG) particularly stands out. Nitrogen atoms can break the undifferentiated structure of graphene and open the bandgap while endowing graphene with an uneven electron density distribution. Therefore, NG retains nearly all the advantages of original graphene and is equipped with several novel properties, ensuring infinite possibilities for NG-based photocatalysis. This review introduces the atomic and band structures of NG, summarizes in situ and ex situ synthesis methods, highlights the mechanism and advantages of NG in photocatalysis, and outlines its applications in different photocatalysis directions (primarily hydrogen production, CO₂ reduction, pollutant degradation, and as photoactive ingredient). Lastly, the central challenges and possible improvements of NG-based photocatalysis in the future are presented. This study is expected to learn from the past and achieve progress toward the future for NG-based photocatalysis.

Hierarchical WO3 microflowers with tailored oxygen vacancies for boosting photocatalytic dye degradation

Hierarchical WO3 microflowers with tailored surface oxygen vacancies show a remarkably boosted activity toward visible-light-driven photocatalytic dye degradation.

Graphene quantum dots based on maltose as a high yield photocatalyst for efficient photodegradation of imipramine in wastewater samples

PURPOSE

In this work, for the first time, graphene quantum dots (GQDs) based on maltose were fabricated as a new photocatalytic material to the photodegradation of imipramine (as a persistence organic pollutant) under light irradiation.

METHODS

The synthesized GQDs were characterized by different instrumentation approaches such as X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), nitrogen adsorption/desorption, and transmission electron microscopy (TEM). A Box-Behnken design (BBD) and the response surface methodology (RSM) were applied for the optimization of different factors that affect the overall photocatalytic yield.

RESULTS

Under the optimized conditions (pH of the sample solution: 2.0; photocatalyst dosage: 0.1 mg mL^-1; UV exposure time: 80 min), the highest achievable reduction efficiency was obtained about 80%. The stability and reusability of the synthesized photocatalytic material were investigated in four reaction cycles (80 min), which showed only a 15% photo-activity loss after the fourth photocatalytic runs.

CONCLUSIONS

The proposed method was successfully applied to degrade the mentioned drug in the real wastewater samples by about 70%. Regarding the mentioned advantages by the proposed method, this new kind of photocatalytic material possesses a strong potential for photodegradation of pollutants in industrial wastewater samples.

GRAPHICAL ABSTRACT

Photodegradation of imipramine using graphene quantum dots based on maltose.

Tuning the properties of boron-doped reduced graphene oxide by altering the boron content

Boron-doping enhanced the occurrence of the energy bandgap, the pore structure and interfacial charge transfer characteristics.

Fullerene-Directed Synthesis of Flowerlike Cu3(PO4)2 Crystals for Efficient Photocatalytic Degradation of Dyes

Biomineralization is a typical methodology developed by nature to produce calcium-based materials. A method mimicking this process has nowadays become popular for the preparation of artificial organic-inorganic hybrids. Here, Cu₃(PO₄)₂ crystals with a flowerlike morphology have been prepared using water-soluble derivatives of fullerene C₆₀ as templates. In a typical system, flowerlike crystals of Cu₃(PO₄)₂ (denoted FLCs-Cu) were obtained by simply dropping an aqueous solution of CuSO₄ into phosphate-buffered saline (PBS) containing a highly water-soluble multiadduct of C₆₀ (fullerenol). The best condition for the preparation of FLCs-Cu appeared at 0.20 mg·mL^-1 fullerenol and 0.10 mol·L^-1 PBS. During the formation of FLCs-Cu, fullerenol acts as a template and its content in FLCs-Cu is trace (less than 5% by atom) as confirmed by scanning electron microscopy mapping and thermogravimetric analysis. This feature makes fullerenol reusable, and the FLCs-Cu can be prepared repeatedly using the same fullerenol aqueous solution at least 10 times without a noticeable change in the morphology. The N₂ adsorption/desorption isotherm showed that the doping of fullerenol increased the specific surface area of the Cu₃(PO₄)₂ crystal. When fullerenol was replaced by C₆₀ monoadducts that are cofunctionalized with a pyrrolidine cation and oligo(poly(ethylene oxide)) chains, FLCs-Cu can form as well, indicating that the strategy of using water-soluble C₆₀ derivative as a template to get FLCs-Cu is universal. As a typical example of practical applications, the photocatalytic activity of the FLCs-Cu was investigated toward the degradation of dyes including rhodamine B and rhodamine 6G. In both cases, efficient photodegradation has been confirmed.

Visible-Light Driven TiO₂ Photocatalyst Coated with Graphene Quantum Dots of Tunable Nitrogen Doping

Nitrogen doped graphene quantum dots (NGQDs) were successfully prepared via a hydrothermal method using citric acid and urea as the carbon and nitrogen precursors, respectively. Due to different post-treatment processes, the obtained NGQDs with different surface modifications exhibited blue light emission, while their visible-light absorption was obviously different. To further understand the roles of nitrogen dopants and N-containing surface groups of NGQDs in the photocatalytic performance, their corresponding composites with TiO₂ were utilized to degrade RhB solutions under visible-light irradiation. A series of characterization and photocatalytic performance tests were carried out, which demonstrated that NGQDs play a significant role in enhancing visible-light driven photocatalytic activity and the carrier separation process. The enhanced photocatalytic activity of the NGQDs/TiO₂ composites can possibly be attributed to an enhanced visible light absorption ability, and an improved separation and transfer rate of photogenerated carriers.

Thermally oxidized CdS as a photoactive material

CdS oxidized in wide temperature range shows unique photocatalytic activity both in UV and visible light.

Molecular-Level Understanding of Selectively Photocatalytic Degradation of Ammonia via Copper Ferrite/N-Doped Graphene Catalyst under Visible Near-Infrared Irradiation

Developing photocatalysts with molecular recognition function is very interesting and desired for specific applications in the environmental field. Copper ferrite/N-doped graphene (CuFe2O4/NG) hybrid catalyst was synthesized and characterized by surface photovoltage spectroscopy, X-ray powder diffraction, transmission electron microscopy, Raman spectroscopy, UV–Vis near-infrared diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The CuFe2O4/NG catalyst can recognize ammonia from rhodamine B (RhB) in ammonia-RhB mixed solution and selectively degrade ammonia under visible near-infrared irradiation. The degradation ratio for ammonia reached 92.6% at 6 h while the degradation ratio for RhB was only 39.3% in a mixed solution containing 100.0 mg/L NH3-N and 50 mg/L RhB. Raman spectra and X-ray photoelectron spectra indicated ammonia adsorbed on CuFe2O4 while RhB was adsorbed on NG. The products of oxidized ammonia were detected by gas chromatography, and results showed that N2 was formed during photocatalytic oxidization. Mechanism studies showed that photo-generated electrons flow to N-doped graphene following the Z-scheme configuration to reduce O2 dissolved in solution, while photo-generated holes oxidize directly ammonia to nitrogen gas.

Studies on mass production and highly solar light photocatalytic properties of gray hydrogenated-TiO2 sphere photocatalysts

In this paper, it is first reported that gray hydrogenated TiO₂ sphere photocatalysts (H-TiO₂) with high reactivity to solar light are mass produced within a few minutes using an underwater discharge plasma modified sol-gel method at room temperature and atmospheric pressure. This plasma modified system is an easy one-step in-situ synthetic process and the crystallinity, hydrogenation, and spherical structure of H-TiO₂ are achieved by the synergy effect between the continuous reaction of highly energetic atomic and molecular species generated from the underwater plasma and surface tension of water. The resultant H-TiO₂ demonstrated high anatase/rutile bicrystallinity and extended optical absorption spectrum from the ultraviolet (UV) to visible range. Furthermore, various defects including oxygen vacancies and hydroxyl species on the TiO₂ surface permitted the enhancement of the photocatalytic performance. It was demonstrated that H-TiO₂ photocatalysts showed significant degradation efficiencies for reactive black 5 (RB 5), rhodamine B (Rho B), and phenol (Ph) under solar light irradiation, up to approximately 5 times higher than that of commercial anatase TiO₂ (C-TiO₂), which resulted in good water purification. Notably, it was also possible to cultivate HepG2 cells using such well-purified water (to degrees up to 76%), with minimal cytotoxicity. Considering all these results, we believe that this novel plasma technology is promising for important environmental applications.

Visible light induced degradation of pollutant dyes using a self-assembled graphene oxide–molybdenum oxo-bis(dithiolene) composite

An easily separable graphene oxide–molybdenum oxo-bis(dithiolene) ([Ph₄P]₂[MoO(S₂C₂(CN)₂)₂]) composite degraded Rhodamine B and Rose Bengal dye upon visible light exposure.

Controlling electronic properties of MoS2/graphene oxide heterojunctions for enhancing photocatalytic performance: the role of oxygen

The manipulation of the constituents of novel hetero-photocatalysts is an effective method for improving photocatalytic efficiency, but a theoretical understanding of the relationship between interlayer interaction and photocatalytic activity is still lacking.

Determination of graphene's edge energy using hexagonal graphene quantum dots and PM7 method

Graphene quantum dots (GQDs) are important for a variety of applications and designs, and the shapes of GQDs rely on the energy of their boundaries.

New Understanding on Photocatalytic Mechanism of Nitrogen-Doped Graphene Quantum Dots-Decorated BiVO4 Nanojunction Photocatalysts

Bismuth vanadate (BiVO₄) is a promising candidate as a visible-light-driven photocatalyst in the aspect of practical applications. To investigate the origin of active species from BiVO₄ and understand the influence of the variations of the photocatalytic process, comparative studies on zero-dimensional nitrogen-doped graphene quantum dot (NGQD)-decorated BiVO₄ have been carried out for methylene blue photodegradation. It was found that the hydroxyl group-rich NGQD surface and the established heterojunction structure between NGQDs and BiVO₄ were greatly beneficial for the conversion of the ^•OH radical. With NGQD decoration, the dominant oxidant species for NGQDs/BiVO₄ were confirmed to be ^•OH and H₂O₂, rather than holes originating from the valence band of unmodified BiVO₄. The synergistic photocatalytic mechanism with respect to the interfacial charge transport and the conversion of active species was proposed. The achievement of the controllable active species significantly altering the activity may be applied for different photocatalytic reactions.