Photo-assisted electrochemical detection of bisphenol A in water samples by renewable {001}-exposed TiO2 single crystals

An ultrasensitive probe-free electrochemical immunosensor for gibberellins employing polydopamine-antibody nanoparticles modified electrode

Gibberellins (GA₃) is an ubiquitous plant hormone, which plays a regulatory role in different growth stages of plants, so it is of great significance to develop a sensitive quantitative analysis method for GA₃. In this study, carboxylated graphene oxide- carboxylated multi-walled carbon nanotubes-Fc (GO-MWNT-Fc) composite material and PDANPs-antibody (PDANPs-Ab) were sequentially modified to screen-printed electrodes (SPEs), and an ultrasensitive probe-free immunosensor for GA₃ was developed. Fc was applied to generate electrochemical signals. GO-COOH and MWNT-COOH can increase the catalytic ability of the sensor and bind the PDANPs-Ab nanoparticles. PDANPs nanomaterial were synthetized by a facile self-polymerization and used to bind with antibody, so as to increase the antibody loading of the sensor. The as-prepared immunosensor has the widest detection range (100 aM-1 mM) and lowest detection limit (17.4 aM) for GA₃ up to date. To our knowledge, it is the first electrochemical immunosensor for GA₃. By changing the GA₃ antibody to ABA antibody, a sensitive and selective immunosensor for ABA was also fabricated. This immunosensor platform is simple, sensitive, and low cost. It opens broad prospect in on-site applications for biosensors in detecting of various biomolecules in precision agriculture.

Improving Wastewater Treatment by Triboelectric-Photo/Electric Coupling Effect

The ability to meet higher effluent quality requirements and the reduction of energy consumption are the biggest challenges in wastewater treatment worldwide. A large proportion of the energy generated during wastewater treatment processes is neglected and lost in traditional wastewater treatment plants. As a type of energy harvesting system, triboelectric nanogenerators (TENGs) can extensively harvest the microscale energies generated from wastewater treatment procedures and auxiliary devices. This harvested energy can be utilized to improve the removal efficiency of pollutants through photo/electric catalysis, which has considerable potential application value in wastewater treatment plants. This paper gives an overall review of the generated potential energies (e.g., water wave energy, wind energy, and acoustic energy) that can be harvested at various stages of the wastewater treatment process and introduces the application of TENG devices for the collection of these neglected energies during wastewater treatment. Furthermore, the mechanisms and catalytic performances of TENGs coupled with photo/electric catalysis (e.g., electrocatalysis, photoelectric catalysis) are discussed to realize higher pollutant removal efficiencies and lower energy consumption. Then, a thorough, detailed investigation of TENG devices, electrode materials, and their coupled applications is summarized. Finally, the intimate coupling of self-powered photoelectric catalysis and biodegradation is proposed to further improve removal efficiencies in wastewater treatment. This concept is conducive to improving knowledge about the underlying mechanisms and extending applications of TENGs in wastewater treatment to better solve the problems of energy demand in the future.

A photo-renewable ZIF-8 photo-electrochemical sensor for the sensitive detection of sulfamethoxazole antibiotic

Electroanalysis is an effective monitoring method for organic pollution in environmental samples. However, chemical fouling with the formation of non-conductive fouled films easily occurs on the surface of the electrode during organic pollution detection that would inactivate the electrode and affect the detecting sensitivity of organic pollution. In this work, we found that zeolitic imidazolate framework-8 (ZIF-8) electrode can achieve effective degradation of non-conductive fouled films under the light illumination during electrochemical detection of some typical organic pollution (sulfamethoxazole (SMX), Bisphenol A (BPA) and diclofenac sodium (DS)). Profiting from the charge transfer capability and photoelectric characteristics, ZIF-8 electrode exhibits a lower detection limitation for organic pollution detection and superior regeneration property. The nice detection and superior regenerated property are mainly due to non-selective superoxide radical (·O₂^-) and hydroxyl radicals (·OH) mediation produced by ZIF-8 electrode under light illumination that can mineralize anodic fouled products and resume surface reactive sites. Compared with the single electrochemical determination, photo-assisted electroanalysis provides a stable monitoring and a renewable pathway for practical applications.

In-site synthesis of an inorganic-framework molecular imprinted TiO2/CdS heterostructure for the photoelectrochemical sensing of bisphenol A

In this study, we develop a highly sensitive and selective photoelectrochemical (PEC) sensor for bisphenol A (BPA) determination by combining a TiO₂/CdS heterostructure with inorganic framework molecular imprinting (MI) technology. A MI-TiO₂/CdS heterostructure was synthesized via successive ionic layer adsorption combined with an inorganic framework molecular imprinting method. Due to the matched energy level distribution of TiO₂ with CdS, the formed heterojunction promotes photogenerated charge separation and enhanced PEC conversion. The MI-TiO₂/CdS based PEC sensor exhibits higher photocurrent responses and perfect selectivity for BPA under simulated sunlight irradiation. Benefiting from the unique heterostructure and special recognition ability of MI-TiO₂/CdS, the photocurrent is linear to the concentration of BPA (range from 1 to 100 pmol L^-1), with a low limit detection of 0.5 pmol L^-1 (S/N = 3). Meanwhile, the detection results show that the PEC sensor exhibits excellent sensitivity, high selectivity, and good stability. Furthermore, the PEC sensor was successfully applied to the real environmental sample detection of BPA, in lake and river water, domestic wastewater and tap water. This PEC sensor exhibits favourable BPA detection, and it is also a promising method by which to measure other similar environmental substances selectively and sensitively in future work.

In situ construction of 3D TiO2 photoelectrode with multilevel facet heterojunctions towards the efficient removal of bisphenol A

An innovative three-dimensional (3D) TiO2 photoelectrode with multilevel facet heterojunctions (FHs) is rationally designed based on in situ 1D rutile TiO2 nanorods with top {111} facets on a Ti mesh substrate. The 3D configuration composed of nanosheets and nanorods is provided with large specific area. The stepped band structure of the multilevel FH gives further impetus to spatial charge separation. The obtained FH-{111}TiO2/Ti photoelectrode achieves a 100% removal of bisphenol A (BPA) in only 20 min and presents an outstanding stability even after 10 cycles. Briefly, this work provides a reference pathway for the highly efficient removal of BPA.

Real time detection and monitoring of 2, 4-dinitrophenylhydrazine in industrial effluents and water bodies by electrochemical approach based on novel conductive polymeric composite

Much attention has been given to detection and monitoring of hydrazine-based compounds in recent time because of its significant negative impacts on human health and ecosystem (aquatic lives). This prompted the current study focusing on detection of 2, 4-dinitrophenylhydrazine (2, 4-dnphz) using electrochemically synthesized poly-para amino benzoic acid-manganese oxide (P-pABA-MnO₂) composite film. The synthesized P-pABA-MnO₂ composite film was characterized in terms of its structural and morphological properties by X-ray diffraction spectroscopy and field emission scanning electron microscopy respectively. In addition, functionalities and binding energy of p-PABA-MnO2 were confirmed using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy respectively. Finally, electrochemical properties were investigated using electrochemical impedance spectroscopy and cyclic voltammetry. The synthesized P-pABA-MnO₂ displayed good electrocatalytic reduction property towards 2, 4-dnphz with ultra-low limit of detection (0.08 μM; S/N = 3) and very high sensitivity (52 μAμ^-1Mcm^-2). The proposed sensor based on P-pABA-MnO₂ also demonstrated good stability in terms of repeatability, reproducibility and interferents effects. Lastly, the proposed sensor was satisfactorily used in detection of 2, 4-dnphz in environmental real samples.

Highly Characteristic Adsorption Based on Single Crystal {001}-TiO2 Surface Molecular Recognition Promotes Enhanced Oxidation

Exploring the adsorption and selective removal mechanism of target pollutants on the catalytic interface is an important research topic in the field of environmental sewage treatment. However, the molecular recognition based on the surface of single crystals is still unclear. Single crystal molecularly imprinted TiO₂ (001-MI-TiO₂) with a highly exposed {001} plane was prepared by a hydrothermal method to characteristically adsorb and degrade phenol. The kinetics of phenol oxidation on 001-MI-TiO₂ was 12.93 times that of polycrystal nonimprinted TiO₂. The phenol adsorption quantity of 001-MI-TiO₂ was 1.68 times that of the polycrystal molecularly imprinted TiO₂ (MI-TiO₂). Compared with MI-TiO₂, the significantly increased removal of phenol on 001-MI-TiO₂ mainly attributed to the enhanced adsorption quantity and better photocatalytic performance. The recognition mechanism of phenol on the 001-MI-TiO₂ during the adsorption process was studied using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), which indicated enhanced adsorption of phenol when compared with MI-TiO₂. The recognition between the phenol molecule and the imprinted sites mainly relied on the hydrogen bond between the π bond of the benzene ring and the hydroxyl group on the surface of TiO₂. Besides, the interferent ATR-FTIR results showed that the single crystal surface can significantly reduce noncharacteristic adsorption, indicating good selectivity for the targets. In addition, the degradation intermediates during the photocatalytic process were further analyzed by in situ infrared technology.

Stable Electrochemical Determination of Dopamine by a Fluorine-Terminated {001}-Exposed TiO2 Single Crystal Sensor

Photochemical oxidation is able to effectively regenerate the fouled electrode in electrochemical pollutant monitoring, while its regeneration capacity is limited by the surface-bound hydroxyl radical speciation with low activity and mobility, which is attributed to the dissociated water adsorption on hydrophilic metal oxides. In this work, fluorine-terminated {001}-exposed TiO₂ single crystals (F-TiO₂) are rationally designed to construct an Au-based electrochemical sensor (Au/F-TiO₂) for dopamine (DA) detection in different matrices. The Au/F-TiO₂ sensor exhibits an efficient and stable detection capacity in both environmental and biological samples. A superior photochemical regeneration capacity is obtained on the Au/F-TiO₂ electrode with much reduced matrix effects under UV irradiation. Spectral observation, crystallographic analysis, pollutant degradation performance, radical inhibition, and surface enhanced Raman scattering tests reveal that both the fluorine-terminated surface chemical features and the bulk-free radical speciation are mainly responsible for the superior photochemical regeneration capacity of the Au/F-TiO₂ electrode. Even for the real biological samples, a stable electrochemical DA detection is also achieved on the Au/F-TiO₂ sensor. Our work establishes a new approach to refine electrochemical sensors for stable monitoring and provides a robust photoactive electrode substrate with high efficiency and low cost for practical applications.

Recycling of titanium-coagulated algae-rich sludge for enhanced photocatalytic oxidation of phenolic contaminants through oxygen vacancy

In the 21st century, sludge disposal and resource recycling are global issues. Titanium coagulation has received increasing attention due its strong coagulation capability and sludge recycling. Titanium coagulation is highly efficient for the treatment of algae-laden micro-polluted surface water; however, the safe disposal of titanium-coagulated algae-rich sludge remains a challenge. Here, we report on the recycling of titanium-coagulated algae-rich sludge for the production of functional TiO₂ nanoflowers (TNFs) through a simple hydrothermal and calcination process. Anatase TNFs (particle size of 10-15 nm) with petal-like structures (mesoporous), relatively high specific surface areas, i.e. 299.4 m²g^-1, and low band gaps, i.e. 2.67 eV (compared to P-25), were obtained. Additionally, oxygen vacancy (OV) was generated on the surface of the recycled TNFs based on electron paramagnetic resonance (EPR) results, which were verified by the first-principles calculations within density-functional theory. These TNFs display high photocatalytic performance for the degradation of diverse phenolic organic contaminants, such as bisphenol A, diphenyl phenol, p-tert-butyl phenol, and resorcinol, i.e. > 95%, under mild ultraviolet light irradiation and without any sacrificial reagents. Formation of OV on TNFs not only efficiently inhibited the recombination of photo-generated electrons and holes but also facilitated contaminant adsorption and photo-generated electron transfer on the surface of the recycled TNFs, thereby promoting the generation of holes and hydroxyl and superoxide radicals which were regarded as the reactive oxygen species for attacking contaminants in the reactions. This study proposes a new perspective on recycling chemical-coagulated sludge for producing functional nanomaterials as photocatalysts.