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A Box–Behnken design (BBD) for a response surface methodology with five factors and three levels was applied to design 2,4-D degradation experiments under visible light. To optimize the experimental conditions, the five factors included the amount of Cdots in a Cdots (x%)-ZnBi2O4 catalyst (x = 0–2%), the decomposition time (90–120 min), the initial 2,4-D concentration (30–40 mg/L), the catalyst dosage (0.5–1.5 mg/L), and the pH (2–7), and these were selected as independent variables. The BBD method proposed a second-order polynomial equation that fitted the experimental data perfectly. The results of the analysis of variance (ANOVA) confirmed the appropriateness of the proposed model, resulting in the relationship between the predicted and adjusted values having an R2 value of 0.9980. The optimal conditions for the photodecomposition of 2,4-D were found to be an initial 2,4-D concentration of 30 mg/L, a degradation time of 120 min, a Cdots(2%)-ZnBi2O4 dosage of 1.0 mg/L, and a pH of 4.0. Under these conditions, the highest 2,4-D photodecomposition of 91.1% was obtained, which was in reasonable agreement with the predicted value of 91.67%. After 6 consecutive reaction cycles, the photodecomposition efficiency still exceeded 81%. The results confirmed that the Cdots(2%)-ZnBi2O4 photocatalyst has excellent reusability. Moreover, the lowest concentration of Cdots(2%)-ZnBi2O4 that inhibited the growth of E. coli (ATCC 8793) and S. aureus (ATCC 6538) was 150 µg/mL, with an inhibition zone of 18–19 nm for E coli and about 15 mm for S. aureus. [ABSTRACT FROM AUTHOR]

The narrow band gap and rapid recombination rate of photogenerated carriers in CuBi2O4 limits the photocatalytic performance. Because it possesses unique properties such as up-conversion photoluminescence (PL) and in-plane quantum confinement effect, graphitic carbon nitride quantum dots (CNQDs) have outstanding application prospects in many fields. By combining solid-phase, coprecipitation and reconstruction methods, a new Z-scheme CNQDs/CuBi2O4 photocatalyst was successfully fabricated. The Box–Behnken design was optimized to study the complex interaction between reaction parameters. The CNQDs percentage in the catalyst, reaction time, 2,4-Dichlorophenoxyacetic acid (2,4-D) concentration, catalyst dose, and pH were varied from 0 to 2%, 90 to 120 min, 30 to 40 mg/L, 0.5 to 1.5 g/L, and 2.0 to 7.0, respectively, to maximize the 2,4-D removal efficiency after exposure to visible light. The following reaction parameters led to the highest photocatalytic removal efficiency: 1.0% of CNQDs, 110 min of reaction time, 33.0 mg/L of 2,4-D, 1.0 g/L of CNQDs/CuBi2O4, and a pH of 4.78. The predicted efficiency of 94.34% was very close to the experimental efficiency of 92.35%, which confirmed the accuracy of the design. The excellent activity of the CNQDs(1%)/CuBi2O4 catalyst in the photocatalytic degradation of 2,4-D is due to the enhanced charge separation efficiency and improved light absorption in the Z-scheme heterojunctions. Additionally, CNQDs(1%)/CuBi2O4 can be recycled with outstanding stability over four consecutive cycles. Superoxide radical (•O2−) and photoinduced hole (h+) play major roles, while the hydroxyl radical (OH•) plays a minor role in the photodegradation process. This study demonstrates that the design of the heterojunction is effective in achieving superior photocatalytic performance. The newly-developed Z-scheme CNQDs(1%)/CuBi2O4 photocatalyst is a promising visible-light catalyst for the decomposition of organic pollutants. [ABSTRACT FROM AUTHOR]

Upconversion fluorescence is the process of converting optical energy from low absorption energies to high emission energies. The upconversion (UC) materials exhibit significant advantages such as high penetration depth, low unwanted autofluorescence and light scattering from biological species at near-infrared excitation. Nowadays, UC materials are widely applied in optical applications, including solid-state lasers, temperature sensor and chemical sensors. The upconversion materials consist of low phonon host material and sensitizer-activator pair. The sensitizer and activator are often rare earth elements, where energy transfers from the sensitizer to the activator. This review describes the general picture and recent progress of lanthanide upconversion fluorescent materials along with applications in biochemical sensing and imaging. We also provide novel strategies to enhance upconversion intensity and tunable emissions with doping metal ions and core-shell structures, and to integrate magnetic properties to upconversion materials. [ABSTRACT FROM AUTHOR]