Effects of nitrogen/bismuth-doping on the photocatalyst composite of carbon dots/titanium dioxide nanoparticles (CDs/TNP) for enhanced visible light-driven removal of diclofenac

Tailoring structural and optical properties of Cu(II)-induced MgAl2O4 nanoparticles and their response to toxic dyes under solar illumination

Worldwide environmental challenges pose critical problems with the growth of the global economy. Addressing these issues requires the development of an eco-friendly and sustainable catalyst for degrading organic dye pollutants. In this study, copper-doped magnesium aluminates (CuxMg1-xAl2O4) with x = 0.0-0.8 were synthesized using a citrate-based combustion route. The inclusion of Cu(II) significantly impacted the structural, microstructural, optical, and photocatalytic activity of the catalyst. Rietveld analysis of X-ray diffraction powder profiles revealed single-phase spinels crystallized in the face-centered cubic unit cell with Fd 3 ¯ m space group. Chemical states of the ions, surface morphology, and elemental investigation were analyzed by X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. UV-visible and diffuse reflectance spectroscopies confirmed the reduction of the band gap due to Cu(II) doping, validated by first-principle investigations using the WIEN2k code. The catalyst with x = 0.8 showed higher photocatalytic efficacy (90% and 93%) for removing two azo organic dye pollutants, rhodamine B and methyl orange, respectively, within 120 min. Degradation kinetics followed a pseudo-first-order mechanism. The doped (0.8) sample was structurally and morphologically stable and reusable under visible irradiation, retaining performance after three runs. Scavenger studies confirmed hydroxyl and superoxide radicals' involvement in the degradation. This work presents an effective approach to enhancing CuxMg1-xAl2O4 catalysts' photodegradation performance, with potential applications in pharmaceuticals and wastewater remediation.

An oxygen vacancy-rich BiO2-x/COF heterojunction for photocatalytic degradation of diclofenac

A BiO2-x/COF composite was successfully synthesized by simple mechanical ball milling. Compared to pure BiO2-x and COFs, the BiO2-x/COF composite (1 : 9) showed superior photocatalytic capability. Under visible light irradiation for 90 min, the photocatalytic degradation rate of DCF reached 97%. In addition, the characterization results showed that the formation of heterojunctions and the increase in oxygen vacancy concentration were the reasons for the enhancement of the photocatalytic activity. It is confirmed by free radical capture experiments that ˙O2- and h+ are the main reactive substances in the photocatalytic process. The photocatalytic degradation mechanism of the composite and the photocatalytic degradation pathway of diclofenac were deduced.

SU-101 for the removal of pharmaceutical active compounds by the combination of adsorption/photocatalytic processes

Pharmaceutical active compounds (PhACs) are some of the most recalcitrant water pollutants causing undesired environmental and human effects. In absence of adapted decontamination technologies, there is an urgent need to develop efficient and sustainable alternatives for water remediation. Metal-organic frameworks (MOFs) have recently emerged as promising candidates for adsorbing contaminants as well as providing photoactive sites, as they possess exceptional porosity and chemical versatility. To date, the reported studies using MOFs in water remediation have been mainly focused on the removal of a single type of PhACs and rarely on the combined elimination of PhACs mixtures. Herein, the eco-friendly bismuth-based MOF, SU-101, has been originally proposed as an efficient adsorbent-photocatalyst for the elimination of a mixture of three challenging persistent PhACs, frequently detected in wastewater and surface water in ng L-1 to mg·L-1 concentrations: the antibiotic sulfamethazine (SMT), the anti-inflammatory diclofenac (DCF), and the antihypertensive atenolol (At). Adsorption experiments of the mixture revealed that SU-101 exhibited a great adsorption capacity towards At, resulting in an almost complete removal (94.1 ± 0.8% for combined adsorption) in only 5 h. Also, SU-101 demonstrated a remarkable photocatalytic activity under visible light to simultaneously degrade DCF and SMT (99.6 ± 0.4% and 89.2 ± 1.4%, respectively). In addition, MOF-contaminant interactions, the photocatalytic mechanism and degradation pathways were investigated, also assessing the toxicity of the resulting degradation products. Even further, recycling and regeneration studies were performed, demonstrating its efficient reuse for 4 consecutive cycles without further treatment, and its subsequent successful regeneration by simply washing the material with a NaCl solution.

Carbon Dot-Modified Branched TiO2 Photoelectrochemical Glucose Sensors with Visible Light Response

The development of a photoelectrochemical (PEC) sensor for the sensitive and rapid detection of glucose is highly desirable. In PEC enzyme sensors, inhibition of the charge recombination of electrode materials is an efficient technique, and detection in visible light can prevent enzyme inactivation due to ultraviolet irradiation. In this study, a visible light-driven PEC enzyme biosensor was proposed, using CDs/branched TiO₂ (B-TiO₂) as the photoactive material and glucose oxidase (GOx) as the identification element. The CDs/B-TiO₂ composites were produced via a facile hydrothermal method. Carbon dots (CDs) can not only act as photosensitizers but also inhibit photogenerated electron and hole recombination of B-TiO₂. Under visible light, electrons in the carbon dots flowed to B-TiO₂ and further to the counter electrode through the external circuit. In the presence of glucose and dissolved oxygen, H₂O₂ generated through the catalysis of GOx could consume electrons in B-TiO₂, causing a decrease in photocurrent intensity. Ascorbic acid was added to ensure the stability of the CDs during the test. Based on the variation of the photocurrent response, the CDs/B-TiO₂/GOx biosensor presented a good sensing performance of glucose in visible light, its detection range was from 0 to 9.00 mM, and the detection limit was 0.0430 mM.

Enhanced Photocatalytic Kinetics Using HDTMA Coated TiO2-Smectite Composite for the Oxidation of Diclofenac under Solar Light

Slow kinetics is one of the capital issues of photocatalytic technology because of its heterogeneous nature, which involves multi-step processes. Herein, we show that the simple modification of the sol-gel-based TiO2-smectite composite by hexadecyltrimethylammonium bromide (HDTMA) significantly boosts adsorption and photocatalytic efficient sol-gel-based light towards the removal of diclofenac from water. Three photocatalysts were prepared, including TiO2, TiO2-smectite, and HDTMA-TiO2-smectite. The materials were characterized to understand the surface interaction and crystal characteristics. In terms of photoactivity, it was found that the addition of HDTMA to TiO2-smectite improved the removal rate by twice. HDTMA changes the functional groups to TiO2-smectite composite allowing enhanced adsorption and photoactivity through the so-called Adsorb and Shuttle process. The recycling tests show that HDTMA-TiO2-smectite can be used up to four times with good performance. This modification approach could intensify the removal of pollutants from water instead of using complicated and costly techniques.

Response surface methodology optimization for the synthesis of N, S-codoped carbon dots and its application for tetracyclines detection

In this study, using a convenient one-pot microwave-assisted method, we rapidly fabricated a N, S-codoped fluorescent carbon dots (NSCDs) through using citric acid (CA) and _d-penicillamine (DPA) for the detection of tetracyclines (TC). To rapidly and efficiently optimize the various synthesis parameters and significantly decrease the number of experimental runs, the effect of the synthesis factors on quantum yield (QY) by NSCDs was implemented through means of response surface methodology (RSM). The as-synthesized NSCDs presented superior photoluminescence stability with a strong quantum yield (QY) of 91.55% under optimal conditions, which was consistent with the predicted value using RSM. The fluorescence intensity of the NSCDs could be quenched effectively after adding TC by the inner filter effect (IEE) and photoinduced electron transfer (PET). Thus, the determination of TC by using NSCDs as a facile fluorescent probe was constructed in the range of 0.2-70 μM with a limit detection of 0.072 μM. Moreover, this detection approach has been utilized to detect TC in actual samples with satisfactory results.