Unique Up-converted Photoluminescence Research Articles

Enhanced photocatalytic gaseous formaldehyde degradation using N-CQDs/OVs-TiO2 composite under visible light: Unraveling the synergistic effects of N-CQDs and oxygen vacancies

Limited utilization of photogenerated charge carriers in titanium dioxide under visible light have hinder its application development. To address this challenge, a novel N-doped carbon quantum dots (N-CQDs) and oxygen vacancies (OVs) synergistically decorated on TiO2 (P25) was synthesized through a facile one-step hydrothermal method. Under visible light irradiation, the first order reaction rate constants of formaldehyde (HCHO) photocatalytic oxidation by OVs-TiO2 and N-CQDs/OVs-TiO2 was significantly higher than that of pristine P25, with 10.1 and 16.7 folds increase, respectively. Characterization results confirmed the generation of OVs on the surface of N-CQDs/TiO2 composite. The optical and electrochemical experiments suggested the electron capture center effect of OVs and the properties of N-CQDs in unique up-converted photoluminescence, efficient charge separation, as well as significant adsorption in visible light region. In addition, the work function also clarified that photoelectrons could transfer from N-CQDs to OVs-TiO2. Furthermore, different relative humidity and electron paramagnetic resonance (EPR) experiments demonstrated that the hydroxyl radical (•OH) was the dominant reactive radical in HCHO photodegradation. The •O2− could also enhance the photodegradation efficiency of HCHO. This work provides an in-depth understanding on the complementary roles of N-CQDs and OVs and is helpful for designing metallic oxide photocatalysts for volatile organic compounds removal.

Extensive solar light harvesting by integrating UPCL C-dots with Sn2Ta2O7/SnO2: Highly efficient photocatalytic degradation toward amoxicillin

The carbon dots (C-dots) mediated Sn2Ta2O7/SnO2 heterostructures with spongy structure were successfully assembled by simple hydrothermal route. The photocatalytic removal efficiency of amoxicillin (AMX, 20 mg L−1) over C-dots/Sn2Ta2O7/SnO2 was estimated to reach up 88.3% within 120 min simulated solar light irradiating. Meanwhile, the HPLC-MS/MS analysis and density functional theory (DFT) computation were examined to clarify the photo-degradation pathway of AMX. The mechanism investigation proposed that with the modification of C-dots, the photocatalysts improves the utilization of solar energy by harvesting the long wavelength solar light due to their unique up-converted photoluminescence (UCPL). In addition, the porous spongy structure and plenty of tiny C-dots promote the ability of adsorption by enlarged specific surface area. Furthermore, the C-dots mediated Z-type heterojunction of Sn2Ta2O7/SnO2 facilitates the efficient separation and transfer of photo-induced carriers. Our work affords a promising approach for the design of the high-efficient photocatalysts to remedy poisonous antibiotics in aqueous environment.

Efficient degradation of Levofloxacin with magnetically separable ZnFe2O4/NCDs/Ag2CO3 Z-scheme heterojunction photocatalyst: Vis-NIR light response ability and mechanism insight

A highly efficient and easily recoverable catalyst is always desirable for practical photocatalytic applications. In this study, a magnetically separable ZnFe2O4/NCDs/Ag2CO3 Z-scheme heterojunction photocatalyst using nitrogen doped carbon quantum dots (NCDs) as solid-state electron mediators was fabricated by an easy-operated deposition-precipitation method. The prepared ZnFe2O4/NCDs/Ag2CO3 photocatalyst exhibits a promoted photocatalytic activity for Levofloxacin (LVFX) removal compared to single ZnFe2O4 and Ag2CO3, achieving 88.75% and 22.53% degradation efficiency under visible and near-infrared (NIR) light irradiation, respectively. Characterization results show that the synergistic effect of remarkable charge carrier separation efficiency and broadened solar light absorption is responsible for the enhanced photocatalytic performance. The well-matched band structures of the two semiconductors facilitate the charge transfer in Z-scheme transfer model, resulting in high charge separation rate. Simultaneously, due to the superb electron transfer character of NCDs, the introduction of NCDs can further accelerate the transfer of the photo-generated charges as solid-state electron mediators between ZnFe2O4 and Ag2CO3. Furthermore, the unique up-converted photoluminescence properties of NCDs can broaden the optical absorption of the prepared ZnFe2O4/NCDs/Ag2CO3 to NIR region, thus leading to an enhanced utilization of solar energy. This work provides a novel insight into the fabrication of novel all-solid-state Z-scheme photocatalyst based on nitrogen doped carbon quantum dots and opens new vista for the design of magnetically separable and highly efficient photocatalysts for environmental remediation.

Visible-Light Upconversion Carbon Quantum Dots Decorated TiO2 for the Photodegradation of Flowing Gaseous Acetaldehyde

Carbon-modified photocatalyst has attracted extensive attentions in the field of gaseous pollutant removal, mainly due to the improved adsorption properties and electronic transport of carbon matrix, such as carbon nanotubes, graphene, and fullerene, etc. In this work, carbon quantum dots (CQDs) were employed to enhance the photocatalytic performance of TiO2-based composites for flowing gaseous acetaldehyde removal. Besides the aforementioned advantages of carbon materials, the unique up-converted photoluminescence property of CQDs is capable of extending the optical absorption to visible-light range. Moreover, the electron spin resonance (ESR) results firstly verified a stable existence of Ti3+ defect in the CQDs/TiO2 composite, which is possibly induced by the electron migration from CQDs to TiO2. And the formed Ti3+ donor energy level in the band gap could further help with the visible-light harvesting. During the photodegradation experiments, with two-hour continuous flowing gaseous acetaldehyde injection (500 ppm, 20 sccm), the CQDs/TiO2 composite remained 99% removal efficiency under fluorescent lamp irradiation (λ > 380 nm). The optimized CQDs content was obtained as 3 wt%, and the underlying mechanism was further analyzed by temperature programmed desorption (TPD) methods. This work will push forward the air purification researches by providing new insights of CQDs sensitized photocatalyst.

P–n junction induced electron injection type transparent photosensitive film of Cu2O/carbon quantum dots/ZnO

An electron injection type transparent photosensitive Cu2O/carbon quantum dot (C QD)/ZnO p−n junction film was prepared by a simple route in which, successively, the ZnO film was prepared by a sputtering process, the C QDs and Cu2O were prepared by hydrothermal synthetic and chemical methods, then the C QDs and Cu2O were introduced onto the surface of the ZnO film. The results indicated that the C QDs and Cu2O were well combined with the ZnO film. The transparency and photosensitivity of this film were investigated, and exhibited an obvious photosensitive enhancement compared with those of the unmodified film. Through analysis, this enhancement of the photoconductivity could be attributed to the remarkable Cu2O/ZnO p−n junction and C QDs with unique up-converted photoluminescence.

The flexible-transparent photosensitive films of cotton cellulose framework of carbon quantum dots/ZnO

The flexible-transparent photosensitive films of cotton cellulose framework of carbon quantum dots (C QDs)/ZnO were prepared by electrospinning-hydrothermal method. The results demonstrated that these films exhibited obvious enhancement of photosensitivity and flexible stability. Further, this enhanced photoconductivity and flexible stability could be attributed to C QDs with unique up-converted photoluminescence and cotton cellulose with flexibility and physical-chemical stability.

Fabrication of carbon quantum dots modified granular SnO2 nanotubes for visible light photocatalysis

The C QDs modified granular SnO2 nanotubes are prepared via a simple technical route through which SnO2 nanotubes are dispersed in C QDs solution, then dried at 80°C. The results of X-ray photoelectron spectroscopy, Fourier-transform infra-red spectroscopy, transmission electron microscopy indicated that SnO2 nanotubes are well combined with C QDs through surface carbon–oxygen groups. By degradation of Rhodamine B under visible light irradiation, it demonstrates that the photocatalytic performance of these composites significantly enhanced. Furthermore, the unique up-converted photoluminescence behaviour of the carbon dots and the remarkable granular, tube-shape structure of the SnO2 are considered as the main reasons of this enhancement.

The photosensitivity of carbon quantum dots/CuAlO2 films composites

Carbon quantum dots/CuAlO2 films were prepared by a simple route through which CuAlO2 films prepared by sol-gel on crystal quartz substrates were composited with carbon quantum dots on their surface. The characterization results indicated that CuAlO2 films were well combined with carbon quantum dots. The photoconductivity of carbon quantum dots/CuAlO2 films was investigated under illumination and darkness switching, and was demonstrated to be significantly enhanced compared with CuAlO2 films. Through analysis, this enhancement of photoconductivity was attributed to the carbon quantum dots with unique up-converted photoluminescence behavior.

Photovoltaic Conversion Enhancement of a Carbon Quantum Dots/p-Type CuAlO2/n-Type ZnO Photoelectric Device.

Carbon quantum dots (C QDs)/p-type CuAlO2/n-type ZnO photoelectric bilayer film composites were prepared by a simple route, through which ZnO films were sputtered on crystal quartz substrates and CuAlO2 films were prepared by sol-gel on ZnO films and then these bilayer films were composited with C QDs on their surface. The characterization results indicated that C QDs were well combined with the surface of the CuAlO2 films. The photovoltage and photocurrent of these bilayer film composites were investigated under illumination and darkness switching, which demonstrated to be significantly enhanced compared with those of the CuAlO2/ZnO bilayer films. Through analysis, this enhancement of the photoconductivity was mainly attributed to C QDs with unique up-converted photoluminescence behavior.

The visible light catalytic properties of carbon quantum dots/ZnO nanoflowers composites

Carbon quantum dots (C QDs)/ZnO nanoflowers composites were prepared via a simple technical route through which ZnO nanoflowers were prepared by electrospinning-hydrothermal synthesis and dispersed in C QDs solution, then dried at 80 °C. The results indicated that ZnO nanoflowers were well combined with C QDs. The visible light photocatalytic activity of C QDs/ZnO nanoflowers coposite was investigated by degradation of Rhodamine B under visible light irradiation, and it is demonstrated that the photocatalytic performance of this composites was significantly enhanced compared with that of pure ZnO nanoflowers. Furthermore, the unique up-converted photoluminescence behaviour of the carbon dots and the novel 3-D structure of the ZnO were considered as the main reasons of this enhancement.

Preparation of carbon quantum dots/ TiO2nanotubes composites and their visible light catalytic applications

Carbon quantum dots/TiO2 nanotubes composites were prepared by a simple technical route through which TiO2 nanotubes prepared by electrospinning were dispersed in carbon quantum dots solution, and dried at 80 °C. The results indicated that the TiO2 nanotubes composites were combined with the carbon quantum dots. The photocatalytic activity of the carbon quantum dots/TiO2 nanotubes composites was investigated by the degradation of rhodamine B under visible light irradiation, and it was demonstrated to be significantly enhanced compared with that of pure TiO2 nanotubes. Through analysis, this enhancement of visible light photocatalytic activity was attributed to the carbon quantum dots with the unique up-converted photoluminescence behavior.

Preparation and visible light photocatalytic activity of carbon quantum dots/TiO2 nanosheet composites

Carbon quantum dots (C QDs)/TiO2 nanosheet (TNS) composites were prepared by a simple low temperature process in which TNS were dispersed in C QDs solution, and dried at 60°C. The C QDs/TNS composites were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, transmission electron microscopy (TEM) and high-resolution TEM. The results indicated that C QDs were well combined with TNS through surface carbon–oxygen groups. The photocatalytic activity was investigated by degradation of rhodamine B under visible light irradiation. The photocatalytic activity of C QDs/TNS composites was significantly enhanced compared with that of C QDs/P25 composites and pure TNS, which indicated that the unique up-converted photoluminescence behavior of C QDs and highly reactive {001} facets of TNS both played important roles in the enhancement of photocatalytic activity of C QDs/TNS composites.