Ultrasmall Inorganic Mesoporous Nanoparticles: Preparation, Functionalization, and Application

Ultrasmall mesoporous nanoparticles (<50 nm), a unique porous nanomaterial, have been widely studied in many fields in the last decade owing to the abundant advantages, involving rich mesopores, low density, high surface area, numerous reaction sites, large cavity space, ultrasmall size, etc. This paper presents a review of recent advances in the preparation, functionalization, and applications of ultrasmall inorganic mesoporous nanoparticles for the first time. The soft monomicelles-directed method, in contrast to the hard-template and template-free methods, is more flexible in the synthesis of mesoporous nanoparticles. This is because the amphiphilic micelle has tunable functional blocks, controlled molecule masses, configurations and mesostructures. Focus on the soft micelle directing method, monomicelles could be classified into four types, i.e., the Pluronic-type block copolymer monomicelles, laboratory-synthesized amphiphilic block copolymers monomicelles, the single-molecule star-shaped block copolymer monomicelles, and the small-molecule anionic/cationic surfactant monomicelles. This paper also reviews the functionalization of the inner mesopores and the outer surfaces, which includes constructing the yolkshell structures (encapsulated nanoparticles), anchoring the active components packed on the shell and building an asymmetric Janus architecture. Then, several representative applications, involving catalysis, energy storage, and biomedicines are presented. Finally, the prospects and challenges of controlled synthesis and large-scale applications of ultrasmall mesoporous nanoparticles in the future are foreseen.

Remarkable Enhancement of Photocatalytic Activity of High-Energy TiO2 Nanocrystals for NO Oxidation through Surface Defluorination

The superior photocatalytic activity of TiO2 nanocrystals with exposed high-energy (001) facets, achieved through the use of hydrofluoric acid as a shape-directing reagent, is widely reported. However, in this study, we report for the first time the detrimental effect of surface fluorination on the photoreactivity of high-energy faceted TiO2 nanocrystals towards NO oxidation (resulting in a NO removal rate of only 5.9%). This study aims to overcome this limitation by exploring surface defluorination as an effective strategy to enhance the photocatalytic oxidation of NO on TiO2 nanocrystals enclosed with (001) facets. We found that surface defluorination, achieved through either NaOH washing (resulting in an improved NO removal rate of 23.2%) or calcination (yielding an enhanced NO removal rate of 52%), leads to a large increase in the photocatalytic oxidation of NO on TiO2 nanocrystals with enclosed (001) facets. Defluorination processes stimulate charge separation, effectively retarding recombination and significantly promoting the production of reactive oxygen species, including superoxide radicals (·O2-), singlet oxygen (1O2), and hydroxyl radicals (·OH). Both in situ diffuse reflectance infrared Fourier-transform spectroscopy and density functional theory calculations confirm the higher adsorption of NO after defluorination, thus facilitating the oxidation of NO on TiO2 nanocrystals.

Photocatalytic degradation of sulfonamides in suspensions of coral-like graphene carbon nitride with nitrogen vacancies

Sulfonamides (SNs) belong to a category of broad-spectrum antibiotics, which have attracted growing concerns owing to the adverse effects on ecosystem. In this paper, coral-like graphitic carbon nitrides with nitrogen vacancies were prepared by polymerization of melamine in the presence of NH4Cl, and the effect of NH4Cl amount on the structure and photocatalytic performance of g-C3N4 in degradation of sulfonamide antibiotics such as sulfamethoxazole (SMX), sulfadiazine (SDZ) and sulfathiazole (STZ) was systematically studied. It was found that the addition of NH4Cl results in the formation of coral-like g-C3N4 with nitrogen vacancies, and optimal photocatalyst (PCN-1 sample) prepared with a melamine to NH4Cl mass ratio of 1:1 showed the highest photocatalytic activity towards SNs degradation due to the quick electron-hole migration, efficient separation capacity and excellent photoelectric properties. The electron paramagnetic resonance (EPR) technique was used to determine the reactive oxygen species (ROSs) that are responsible for the degradation of SNs, and the detailed degradation pathway of STZ was proposed according to the identification of the intermediates by liguid chromatography-high resolution mass spectrometry (LC-HRMS).

Multiscale Interface Engineering of Sulfur-Doped TiO2 Anode for Ultrafast and Robust Sodium Storage

Sodium-ion batteries (SIBs) are a promising electrochemical energy storage system; however, their practical application is hindered by the sluggish kinetics and interfacial instability of anode-active materials. Here, to circumvent these issues, we proposed the multiscale interface engineering of S-doped TiO2 electrodes with minor sulfur/carbon inlaying (S/C@sTiO2), where the electrode-electrolyte interface (SEI) and electrode-current collector interface (ECI) are tuned to improve the Na-storage performance. It is found that the S dopant greatly promotes the Na+ diffusion kinetics. Moreover, the ether electrolyte generates much less NaF in the cycled electrode, but relatively richer NaF in the SEI in comparison to fluoroethylene carbonate-contained ester electrolyte, leading to a thin (9 nm), stable, and kinetically favorable SEI film. More importantly, the minor sodium polysulfide intermediates chemically interact with the Cu current collector to form a Cu2S interface between the electrode and the Cu foil. The conductive tree root-like Cu2S ECI serves not only as active sites to boost the specific capacity but also as a 3D "second current collector" to reinforce the electrode and improve the Na+ reaction kinetics. The synergy of S-doping and optimized SEI and ECI realizes large specific capacity (464.4 mAh g-1 at 0.1 A g-1), ultrahigh rate capability (305.8 mAh g-1 at 50 A g-1), and ultrastable cycling performance (91.5% capacity retention after 3000 cycles at 5 A g-1). To the best of our knowledge, the overall SIB performances of S/C@sTiO2 are the best among all of the TiO2-based electrodes.

Increasing the Photocatalytic Hydrogen Generation Activity of CdS Nanorods by Introducing Interfacial and Polarization Electric Fields

Cadmium sulfide (CdS) is a photocatalyst widely used for efficient H2 production under visible light irradiation, due to its narrow bandgap and suitable conduction band position. However, the fast recombination of carriers results in their low utilization. In order to improve photocatalytic hydrogen production, it reports the successful introduction of metallic Cd and S vacancies on CdS nanorods (CdS NRs) by a facile in situ chemical reduction method, using a thermal treatment process. This procedure generates interfacial and polarization electric fields, that significantly improve the photocatalytic hydrogen production performance of CdS NRs in sodium sulfide and sodium sulfite aqueous solutions, under visible light irradiation (λ >420 nm). The introduction of these electric fields is believed to improve charge separation and facilitate faster interfacial charge migration, resulting in a significantly optimized catalyst, with a photocatalytic hydrogen evolution rate of up to 10.6 mmol-1  g-1  h-1 with apparent quantum efficiency (AQE) of 12.1% (420 nm), which is 8.5 times higher than that of CdS. This work provides a useful method to introduce metallic and S vacancies on metal sulfide photocatalysts to build local polarization and interfacial electric fields for high-performance photocatalytic H2 production.

Green-Mediated Synthesis of NiCo2O4 Nanostructures Using Radish White Peel Extract for the Sensitive and Selective Enzyme-Free Detection of Uric Acid

The ability to measure uric acid (UA) non-enzymatically in human blood has been demonstrated through the use of a simple and efficient electrochemical method. A phytochemical extract from radish white peel extract improved the electrocatalytic performance of nickel-cobalt bimetallic oxide (NiCo2O4) during a hydrothermal process through abundant surface holes of oxides, an alteration of morphology, an excellent crystal quality, and increased Co(III) and Ni(II) chemical states. The surface structure, morphology, crystalline quality, and chemical composition were determined using a variety of analytical techniques, including powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and X-ray photoelectron spectroscopy (XPS). The electrochemical characterization by CV revealed a linear range of UA from 0.1 mM to 8 mM, with a detection limit of 0.005 mM and a limit of quantification (LOQ) of 0.008 mM. A study of the sensitivity of NiCo2O4 nanostructures modified on the surface to UA detection with amperometry has revealed a linear range from 0.1 mM to 4 mM for detection. High stability, repeatability, and selectivity were associated with the enhanced electrochemical performance of non-enzymatic UA sensing. A significant contribution to the full outperforming sensing characterization can be attributed to the tailoring of surface properties of NiCo2O4 nanostructures. EIS analysis revealed a low charge-transfer resistance of 114,970 Ohms that offered NiCo2O4 nanostructures prepared with 5 mL of radish white peel extract, confirming an enhanced performance of the presented non-enzymatic UA sensor. As well as testing the practicality of the UA sensor, blood samples from human beings were also tested for UA. Due to its high sensitivity, stability, selectivity, repeatability, and simplicity, the developed non-enzymatic UA sensor is ideal for monitoring UA for a wide range of concentrations in biological matrixes.

Understanding the unique S-scheme charge migration in triazine/heptazine crystalline carbon nitride homojunction

Understanding charge transfer dynamics and carrier separation pathway is challenging due to the lack of appropriate characterization strategies. In this work, a crystalline triazine/heptazine carbon nitride homojunction is selected as a model system to demonstrate the interfacial electron-transfer mechanism. Surface bimetallic cocatalysts are used as sensitive probes during in situ photoemission for tracing the S-scheme transfer of interfacial photogenerated electrons from triazine phase to the heptazine phase. Variation of the sample surface potential under light on/off confirms dynamic S-scheme charge transfer. Further theoretical calculations demonstrate an interesting reversal of interfacial electron-transfer path under light/dark conditions, which also supports the experimental evidence of S-scheme transport. Benefiting from the unique merit of S-scheme electron transfer, homojunction shows significantly enhanced activity for CO₂ photoreduction. Our work thus provides a strategy to probe dynamic electron transfer mechanisms and to design delicate material structures towards efficient CO₂ photoreduction.

Surface Modification of TiO2 by Hyper-Cross-Linked Polymers for Efficient Visible-Light-Driven Photocatalytic NO Oxidation

Solar-driven photocatalysis offers an environmentally friendly and sustainable approach for the removal of air pollutants such as nitric oxides without chemical addition. However, the low specific surface area and adsorption capacity of common photocatalysts restrict the surface reactions with NO at the ppb-level. In this study, imidazolium-based hyper-cross-linked polymer (IHP) was introduced to modify the surface of TiO₂ to construct a porous TiO₂/IHP composite photocatalyst. The as-prepared composite with hierarchical porous structure achieves a larger specific surface area as 309 m²/g than that of TiO₂ (119 m²/g). Meanwhile, the wide light absorption range of the polymer has brought about the strong visible-light absorption of the TiO₂/IHP composite. In consequence, the composite photocatalyst exhibits excellent performance toward NO oxidation at a low concentration of 600 ppb under visible-light irradiation, reaching a removal efficiency of 51.7%, while the generation of the toxic NO₂ intermediate was suppressed to less than 1 ppb. The enhanced NO adsorption and the suppressed NO₂ generation on the TiO₂/IHP surface were confirmed by in situ monitoring technology. This work demonstrates that the construction of a porous structure is an effective approach for efficient NO adsorption and photocatalytic oxidation.

Synergistic effects of holey nanosheet and sulfur-doping on the photocatalytic activity of carbon nitride towards NO removal

Photocatalysis provides a sustainable way for NOx elimination. However, efficient and safe photocatalytic removal of NOx remain a great challenge due to the limited light-harvesting ability and quick recombination of charge carriers. Herein, holey sulfur-doped g-C₃N₄ nanosheets (CNN-S) was reported by directly calcining a mixture of hydrolyzed dicyandiamide and thioacetamide. The specific surface area of the pristine g-C₃N₄ nanosheets (CNN-S0) is 3-4 times higher than bulk g-C₃N₄ (BCN), and the photocatalytic NO removal rate also increased from 17% (BCN) to 35% (CNN-S0). The effect of sulfur content on the photocatalytic performance was systematic studied, and CNN-S0.5 sample exhibits the highest NO removal rate (53%). The high photoreactivity of S-doped g-C₃N₄ nanosheets can be attributed to enhanced visible light absorption, increased specific surface area, and effective separation and transfer of photo-generated charges owing to the synergistic effect of the nanosheet structure and sulfur doping. In addition, density functional theory calculations show that the doping of S is also beneficial to the adsorption and activation of the reactants on CN.

Synergistic effect of cyano defects and CaCO3 in graphitic carbon nitride nanosheets for efficient visible-light-driven photocatalytic NO removal

Photo-oxidation with semiconductor photocatalysts provides a sustainable and green solution for NO_x elimination. Nevertheless, the utilization of traditional photocatalysts in efficient and safe photocatalytic NO_x removal is still a challenge due to the slow charge kinetic process and insufficient optical absorption. In this paper, we report a novel porous g-C₃N₄ nanosheet photocatalyst modified with cyano defects and CaCO₃ (xCa-CN). The best performing sample (0.5Ca-CN) exhibits an enhanced photo-oxidation NO removal rate (51.18 %) under visible light irradiation, largely surpassing the value of pristine g-C₃N₄ nanosheets (34.05 %). Such an enhancement is mainly derived from an extended visible-light response, improved electron excitation and transfer, which are associated with the synergy of cyano defects and CaCO₃, as evidenced by a series of spectroscopic analyses. More importantly, in-situ DRIFTS and density functional theory (DFT) results suggest that the introduction of cyano defects and CaCO₃ enables control over NO adsorption and activation processes, making it possible to implement a preference pathway (NO → NO⁺ → NO₃¯) and reduce the emission of toxic intermediate NO₂. This work demonstrates the potential of integrating defect engineering and insulator modification to design highly efficient g-C₃N₄-based photocatalysts for air purification.

Insight into the mechanism of deep NO photo-oxidation by bismuth tantalate with oxygen vacancies

Deeply photocatalytic oxidation of nitrogen oxides is still difficult to achieve, mainly limited by few intrinsic active sites and inefficient carrier separation of photocatalysts. Accordingly, we develop a simple room temperature tactic to introduce oxygen vacancies (OVs) into Bi₃TaO₇ (BTO). Based on solid experimental and DFT theoretical supports, we explore the mechanism of NO removal over OVs decorated BTO (OVs-BTO). OVs can not only alter the distribution of local electrons to result in the formation of a fast charge transfer channel between OVs and the adjacent Ta atoms, which improves the transport rate of photogenerated carriers; but also function as active sites to adsorb small molecules (NO, O₂ and H₂O), which being activated and positively drive the NO oxidation reaction. In order to investigate a possible reaction path, a combination of in-situ DRIFTS and simulated Gibbs free energy reveals that the intermediate products of OVs-BTO are helpful to promote the deep oxidation of NO to NO₃^-, while pristine BTO is more likely to produce NO₂ intermediate toxic by-products, which greatly hinders the deep photocatalytic oxidation of NO. This work provides insights into the role of OVs in photocatalysts, and also points out a guideline for the mechanism of semiconductor photocatalysts in eliminating gaseous pollutants.

Research progress in metal sulfides for photocatalysis: From activity to stability

Metal sulfides are a type of reduction semiconductor photocatalysts with narrow bandgap and negative conduction band potential, which make them have unique photocatalytic performance in solar-to-fuel conversion and environmental purification. However, metal sulfides also suffer from low quantum efficiency and photocorrosion. In this review, the strategies to improve the photocatalytic activity of metal sulfide photocatalysts by stimulating the charge separation and improving light-harvesting ability are introduced, including morphology control, semiconductor coupling and surface modification. In addition, the recent research progress aiming at improving their photostability is also illustrated, such as, construction of hole transfer heterojunctions and deposition of hole transfer cocatalysts. Based on the electronic band structures, the applications of metal sulfides in photocatalysis, namely, hydrogen production, degradation of organic pollutants and reduction of CO₂, are summarized. Finally, the perspectives of the promising future of metal-sulfide based photocatalysts and the challenges remaining to overcome are also presented.

Photocatalytic oxidation of NO on reduction type semiconductor photocatalysts: effect of metallic Bi on CdS nanorods

We report the first visible light photocatalytic oxidation of NO on CdS nanorods (CdS-NRs), one of the typical reduction type semiconductor photocatalysts. The NO removal rate in a continuous reactor sharply increases from 44% to 58% after in situ deposition of Bi nanoplates on CdS-NRs. The LSPR effect of metallic Bi causes the dramatic production of superoxide radicals (˙O₂^-) and singlet oxygen (¹O₂) that are responsible for the oxidation of NO.

Plasmonic semiconductor photocatalyst: Non-stoichiometric tungsten oxide

Semiconductor photocatalysis has attracted increasing attention due to its potential application in solving the problems related to energy crisis and environmental pollution. As a typical plasmonic semiconductor, non-stoichiometric tungsten oxide (WO_3-X) has invoked significant interest for its unique property and excellent photocatalytic performance. In this review, we briefly introduce the fundamental properties of the WO_3-x, and then summarize the synthesis methods such as solvothermal reaction, solid phase reduction and exfoliation treatment, together with the modification strategies such as doping and constructing homo-/hetero-junctions. Additionally, we emphasize the practical applications of WO_3-x in hydrogen evolution, nitrogen fixation, carbon dioxide reduction, and pollutant degradation. Finally, comprehensive conclusions and perspectives on the fabrication of WO_3-x photocatalyst leading to satisfactory performance are given as well.

An electroporation strategy to synthesize the membrane-coated nanoparticles for enhanced anti-inflammation therapy in bone infection

The cell membrane-coated nanoparticles (MNPs) showed great potential in treating infectious disease due to their superior biofunctions in improving biocompatibility of nanoparticles and neutralization of pathogen or toxins. However, bone infection is accompanied with severe inflammation and bone loss, which also requires anti-inflammatory and osteoconductive treatment. The conventional membrane coating method has to undergo ultrasonication and extrusion procedures, which reduces the functionality of cell membrane and limits the choice of nanoparticles. In this study, we proposed an electroporation-based membrane coating strategy to facilitate the synthesis of MNPs to tackle those problems. Methods: Magnetic composite nanoparticles with osteoconductive Ca3(PO4)2 and bactericidal TiO2 were assembled into macrophages through phagocytosis and then collected to expose in electric field for obtaining macrophage membrane-coating nanoparticles. By using molecular dynamics simulation and materials characterizations, the cell membrane coating efficiency was confirmed. The in vitro anti-bacterial and anti-inflammatory abilities were tested by bacteria culturing and immune cells activation. Then drug-resistant bacteria induced bone infection model was established to verify its in vivo therapeutic effects. Results: The coated membrane prepared through electroporation reserved the integrality of membrane structure and right-sidedness, with more functional proteins. Those led to the superior properties of recognition and adsorption with bacteria, toxins and inflammatory cytokines. Owing to the benefits of electroporation, the MNPs exhibited significant better antibacterial and anti-inflammatory abilities for enhancing the tissue repair process. Conclusion: This study provides a novel self-assembly cell membrane coating strategy by electroporation to construct multifunctional membrane-coating nanoparticles for bone infection treatment. This strategy not only improves the functions of coated membrane, but is also proved to be universal for varies nanoparticles or cells, indicating a great potential for future applications in the bioengineering field.

Fe1 /TiO2 Hollow Microspheres: Fe and Ti Dual Active Sites Boosting the Photocatalytic Oxidation of NO

Recently, single-atom catalysts have aroused extensive attention in fields of clean energy and environmental protection due to their unique activity and efficient utilization of the active atoms. It is of great importance but still remains a great challenge to unveil the effect of single atoms on precise catalysis. Herein, it is reported that doping TiO₂ hollow microspheres (TiO₂ -HMSs) with single atomic Fe can boost the photoreactivity of TiO₂ -HMSs towards NO oxidation due to the synergistic effects of atomically dispersed Fe and bonded Ti atom which act as dual active sites. The atomically dispersed Fe atoms occupy the subsurface Ti vacancies, and the interaction between Ti 3d and Fe 3d orbitals result in the formation of FeTi bond. Single atomic Fe modulates the electronic structure of the bonded Ti atoms by electron transfer, which facilitates the adsorption and activation of NO and O₂ at Fe and bonded Ti sites, respectively. In addition, the introduction of single atomic Fe sharply suppresses the production of toxic NO₂ byproduct. The synergistic effects of the dual active sites then cause a drastic promotion in photocatalytic oxidation of NO.

Three in one: atomically dispersed Na boosting the photoreactivity of carbon nitride towards NO oxidation

Single atomic Na (Na-SA) was successfully anchored on the surface of carbon nitride nanosheets (CN-NSs) by simple direct calcination of the hydrothermally NaHCO₃ pretreated dicyandiamide (DCDA) precursor. The introduction of Na-SA results in the electron transfer from Na to the complex N_2C, not only improving the light absorption and increasing the adsorption ability, but also stimulating the separation of charge carriers, which sharply improves the NO removal rate from 36.8% to 52.5%, and prevents the production of toxic NO₂ by-product. The excellent photo-stability makes Na-SA/NN-NSs a good candidate photocatalyst for air purification.

Removal of aqueous-phase lead ions by dithiocarbamate-modified hydrochar

Hydrochar produced from agricultural and forestry wastes and its application into the environment are very attractive. Herein, a high-efficiency dithiocarbamate-modified hydrochar (DTHC) was prepared successfully and then applied to eliminate Pb(II) from aqueous solutions. DTHC was characterized by various techniques. It was found that dithiocarbamate and amine groups were successfully grafted onto the surface of hydrochar. The surface area of DTHC was 7.94 m²·g^-1, which was four folds less than pristine hydrochar (31.60 m²·g^-1), but its adsorption capacity obviously increased. Adsorption experiments showed that the Pb(II) adsorption process onto DTHC well accorded with pseudo-2nd-order kinetics and Langmuir isotherms. The highest Pb(II) uptake by DTHC at 293 K determined from the Langmuir model was 151.51 mg·g^-1. Fourier transform infrared spectra and X-ray photoelectron spectroscopy verified that dithiocarbamate, carboxylate, amine and sulfonate groups all facilitated the Pb(II) adsorption. The adsorption mechanism was ascribed to the inner-sphere surface complexation of Pb(II) by these groups and to the ion exchange between Pb(II) and Na(I). Thus, DTHC is an effective adsorbent for Pb(II) removal from water.