Removal of PFASs from water by carbon-based composite photocatalysis with adsorption and catalytic properties: A review

Per- and polyfluoroalkyl substances (PFASs) are a class of persistent organic pollutants widely distributed in aquatic environments. The adsorption and photocatalytic methods have been widely used to remove PFASs in water because of their respective advantages. Still, they have apparent defects when used alone. Therefore, the adsorption and photocatalytic technologies are combined through suitable preparation methods, and the excellent properties of the two are used to synergize the treatment of organic pollutants. This strategy of "concentrating" pollutants and then degrading them in a centralized manner plays an essential role in removing trace PFASs. Nevertheless, a review focusing on this kind of adsorption photocatalyst system is lacking. This review will fill this gap and provide a reference for developing a carbon-based composite photocatalyst. Firstly, different carbon-based composite photocatalysts are reviewed in detail, focusing on the differences in various composite materials' excellent adsorption and catalytic properties. Secondly, the factors influencing the removal effect of carbon-based composite photocatalysts are discussed. Thirdly, the removal mechanism of carbon-based composite photocatalysts is summarized in detail. The removal process involves two steps: adsorption and photodegradation. The adsorption process involves multiple cooperative adsorption mechanisms, and photocatalytic degradation includes oxidative and reductive degradation. Fourthly, the comparison of adsorption-photocatalysis with common treatment techniques (including removal rate, range of adaptation, cost, and the possibility of expanding application) is summarized. Finally, the prospects of carbon-based composite photocatalysts for repairing PFASs are given by evaluating the performance of different composites.

TiO2 quantum dots loaded sulfonated graphene aerogel for effective adsorption-photocatalysis of PFOA

With the pollution of perfluoroalkyl substances (PFASs) became increasingly serious, the researches focused on removal of PFASs by adsorption-photocatalysis method has attracted considerable attention. To make the catalyst TiO₂ disperse uniformly as quantum dots onto hydrophobic surface which was liable to attract perfluorooctanoic acid (PFOA), the surfactant sodium dodecyl sulfate (SDS) were used in this work, which not only connected the hydrophilic TiCl₃ to the hydrophobic sulfonated graphene (SG) nanosheets, but also behaved as the molecular template for controlled nucleation and growth of the nanostructured TiO₂. After 3D SG-TiO₂ QD nanosheets were fabricated, a series of 3D SG-TiO₂ QD aerogels were self-assembled by ice-template. TiO₂ uniformly distributed on the surface of SG aerogel at QD size level (2-3 nm) and the size of TiO₂ could be effectively regulated by concentration of SDS. Compared with aggregated TiO₂ material, 3D SG-TiO₂ QD aerogels owned higher adsorption and photocatalytic performance. Benefiting from the hydrophobic surface of 3D SG as well as dispersed TiO₂ QDs, 3D SG-TiO₂ QD could enrich PFOA instantaneously (0.0381/s) and photocatalytic decomposed them effectively (1.898 E^-4/s). PFOA degradation by hole and hydroxyl radicals proceeded via a stepwise mechanism. The column made of 3D SG-TiO₂ QD could remove PFOA persistently in cycles of permeation. 3D SG-TiO₂ QD possessed powerful adsorption-photocatalytic decomposition capability of PFOA and steady reusability performance. The present work highlights the individual roles and synergistic effect of TiO₂ QD and 3D SG for effectively removing PFOA.

Micro-Refractometry and Local-Field Mapping with Single Molecules

The refractive index n is one of the most important materials parameters of solids and, in recent years, has become the subject of significant interdisciplinary interest, especially in nanostructures and meta-materials. It is, in principle, a macroscopic quantity, so its meaning on a length scale of a few nanometers, i.e., well below the wavelength of light, is not clear a priori and is related to methods of its measurement on this length scale. Here we introduce a novel experimental approach for mapping the effective local value [Formula: see text] of the refractive index in solid films and the analysis of related local-field enhancement effects. The approach is based on the imaging and spectroscopy of single chromophore molecules at cryogenic temperatures. Since the fluorescence lifetime T₁ of dye molecules in a transparent matrix depends on the refractive index due to the local density of the electromagnetic field (i.e., of the photon states), one can obtain the local [Formula: see text] values in the surroundings of individual chromophores simply by measuring their T₁ times. Spatial mapping of the local [Formula: see text] values is accomplished by localizing the corresponding chromophores with nanometer accuracy. We demonstrate this approach for a polycrystalline n-hexadecane film doped with terrylene. Unexpectedly large fluctuations of local-field effects and effective [Formula: see text] values (the latter between 1.1 and 1.9) were found.

Noise-Resilient Quantum Computing with a Nitrogen-Vacancy Center and Nuclear Spins

Selective control of qubits in a quantum register for the purposes of quantum information processing represents a critical challenge for dense spin ensembles in solid-state systems. Here we present a protocol that achieves a complete set of selective electron-nuclear gates and single nuclear rotations in such an ensemble in diamond facilitated by a nearby nitrogen-vacancy (NV) center. The protocol suppresses internuclear interactions as well as unwanted coupling between the NV center and other spins of the ensemble to achieve quantum gate fidelities well exceeding 99%. Notably, our method can be applied to weakly coupled, distant spins representing a scalable procedure that exploits the exceptional properties of nuclear spins in diamond as robust quantum memories.