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Layered double hydroxides （LDHs） have been widely used as catalysts owingto their tunable structure and atomic dispersion of high-valence metal ions;however, limited tunability of electronic structure and valence states havehindered further improvement in their catalytic performance. Herein, we reducedultrathin LDH precursors in situ and topotactically converted them to atomicallythick （N2 nm） two-dimensional （2D） multi-metallic, single crystalline alloynanosheets with highly tunable metallic compositions. The as-obtained alloynanosheets not only maintained the vertically aligned ultrathin 2D structure,but also inherited the atomic dispersion of the minor metallic compositions ofthe LDH precursors, even though the atomic percentage was higher than 20%,which is far beyond the reported percentages for single-atom dispersions （usuallyless than 0.1%）. Besides, surface engineering of the alloy nanosheets can finely tunethe surface electronic structure for catalytic applications. Such in situ topotacticconversion strategy has introduced a novel approach for atomically dispersedalloy nanostructures and reinforced the synthetic methodology for ultrathin 2Dmetal-based catalysts.

Ultrasound with deep penetration depth and high security could be adopted in sonodynamic therapy (SDT) by activating sonosensitizers to generate cytotoxic reactive oxygen species (ROS). Herein, two-dimensional (2D) coordination nanosheets composed of Zn 2+ and Tetrakis(4-carboxyphenyl) porphyrin (TCPP) are fabricated. While exhibiting greatly enhanced ultrasound-triggered ROS generation useful for noninvasive SDT, such Zn-TCPP 2D nanosheets show high loading capacity of oligodeoxynucleotides such as cytosine-phosphorothioate-guanine (CpG), which is a potent toll like receptor 9 (TLR9) agonist useful in activating immune responses. Highly effective SDT of primary tumors could release tumor-associated antigens, which working together with Zn-TCPP/CpG adjuvant nanosheets could function like whole-tumor-cell vaccines and trigger tumor-specific immune responses. Interestingly, ultrasound itself could strengthen anti-tumor immune responses by improving the tumor-infiltration of T cells and limiting regulatory T cells in the tumor microenvironment. Thus, SDT using Zn-TCPP/CpG nanosheets after destruction of primary tumors could induce potent antitumor immune responses to inhibit distant abscopal tumors without direct SDT treatment. Moreover, SDT with Zn-TCPP/CpG could trigger strong immunological memory effects to inhibit cancer recurrence after elimination of primary tumors. Therefore, the 2D coordination nanosheet may be a promising platform to deliver potent SDT-triggered immunotherapy for highly effective cancer treatment.

Highlights Two-dimensional mono- and few-layered Ti 3 CNT x MXene nanosheets with extremely high nitrogen content were synthesized. Better performance for hydrogen evolution reaction (HER) than Pt/C catalyst in acidic, neutral and alkaline solutions. Exceptional performance of HER in both acidic and alkaline solutions. A large current density (> 500 mA cm −2 ) has been achieved for HER. Transition metal carbides, known as MXenes, particularly Ti 3 C 2 T x , have been extensively explored as promising materials for electrochemical reactions. However, transition metal carbonitride MXenes with high nitrogen content for electrochemical reactions are rarely reported. In this work, transition metal carbonitride MXenes incorporated with Pt-based electrocatalysts, ranging from single atoms to sub-nanometer dimensions, are explored for hydrogen evolution reaction (HER). The fabricated Pt clusters/MXene catalyst exhibits superior HER performance compared to the single-atom-incorporated MXene and commercial Pt/C catalyst in both acidic and alkaline electrolytes. The optimized sample shows low overpotentials of 28, 65, and 154 mV at a current densities of 10, 100, and 500 mA cm −2 , a small Tafel slope of 29 mV dec −1 , a high mass activity of 1203 mA mg Pt −1 and an excellent turnover frequency of 6.1 s −1 in the acidic electrolyte. Density functional theory calculations indicate that this high performance can be attributed to the enhanced active sites, increased surface functional groups, faster charge transfer dynamics, and stronger electronic interaction between Pt and MXene, resulting in optimized hydrogen absorption/desorption toward better HER. This work demonstrates that MXenes with a high content of nitrogen may be promising candidates for various catalytic reactions by incorporating single atoms or clusters.

Nanoscale metal organic frameworks (NMOFs) with porous structure and inherent biodegradability are attractive nanomedicine platforms. In addition to conventional particulate NMOFs, two-dimensional (2D) NMOFs are emerging as a unique type of NMOFs which however have been relatively less explored for nanomedicine applications. Herein, 2D-NMOFs composed of Zn 2+ and tetrakis(4-carboxyphenyl) porphyrin (TCPP) are fabricated and functionalized with polyethylene glycol (PEG). Compared to their particulate counterpart, such 2D-NMOFs show greatly increased drug loading capacity and enhanced light-triggered singlet oxygen production, promising for chemotherapy and photodynamic therapy (PDT), respectively. Utilizing the porphyrin structure of TCPP, our 2D-NMOFs could be labeled with a diagnostic radioisotope, 99m Tc, for single photon emission computer tomography (SPECT) imaging, which reveals efficient tumor homing of those 2D-NMOFs upon intravenous injection. While offering a remarkable synergistic in vivo antitumor effect for the combined chemo-PDT, such 2D-NMOFs show efficient biodegradation and rapid renal clearance. Our work presents the great promise of 2D-NMOFs for nanomedicine applications.

Achieving high catalytic performance with lower possible cost and higher energetic efficiency is critical for catalytic oxidation of volatile organic compounds (VOCs). However, traditional thermocatalysts generally undergo low catalytic activity and fewer active sites. Herein, this paper synthesizes nearly all-surface-atomic, ultrathin two-dimensional (2D) Co 3 O 4 nanosheets to address these problems through offering a numerous active sites and high electron mobility. The 2D Co 3 O 4 nanosheets (1.70 nm) exhibit catalyzation to the total oxidation of n-hexanal at the lower temperature of T 90% = 202 °C, and at the space velocity of 5.0 × 10 4 h −1 . It is over 1.2 and 6 times higher catalytic activity than that of 2D CoO nanosheets (1.71 nm) and bulk Co 3 O 4 counterpart, respectively. Transient absorption spectroscopy analysis shows that the oxygen vacancy defect traps electrons, thereby preventing the recombination with holes, increasing the lifetime of τ 1 electrons, and making electron-holes reach a nondynamic equilibrium. The longer the electron lifetime is, the easier the oxygen vacancy defects capture electrons. Furthermore, the defects combine with oxygen to form active oxygen components. Compared with the lattice oxygen involved in the reaction of bulk Co 3 O 4 , the nanosheets change the catalytic reaction path, which effectively reduces the activation energy barrier from 34.07 to 27.15 kJ/mol. The changed surface disorder, the numerous coordinatively-unsaturated Co atoms and the high ratio of O ads /O lat on the surface of 2D Co 3 O 4 nanosheets are responsible for the catalytic performance.

Two-dimensional (2D) porous carbon nanosheets (PCNs) have attracted great attention for their combining both the unique properties of 2D materials and the porous features, but the synthesis of PCNs in a simple yet efficient way still remains a great challenge. Herein, N-doped porous two-dimensional carbon nanosheets (NPCNs) with high surface area and pore volume were fabricated successfully by using graphitic carbon nitride (g-C3N4) as a self-sacrificial template. Compared with ZIF-8 only derived microporous carbon supported Ru catalyst, Ru/NPCNs exhibit much higher catalytic performance for the hydrogenation of benzoic acid, giving a TOF of 1136.6 h−1 at 80 °C and 1 MPa H2. This work may provide a new choice for the synthesis of porous two-dimensional carbon nanosheets that possess a promising candidate as the catalyst support.N-doped porous two-dimensional carbon nanosheets (NPCNs) with high surface area and pore volume were fabricated. Ru/NPCNs exhibited high catalytic performance for the hydrogenation of benzoic acid, giving a TOF of 1136.6 h−1 at 80 °C and 1 MPa H2.

Water pollutants of non-biodegradable toxic aromatic dye including Methylene blue (MB) and Rhodamine (RhB) are extremely carcinogenic thiazines used in various industries such as leather industry, paper industry, and the dyeing industry. The presence of dyes in wastewater causes severe threats to human health that are responsible for various harmful chronic or acute diseases and also shows an adverse impact on the environment as it reduces transparency and is harmful to water microorganisms. To overcome severe issues, many traditional techniques have been used to remove toxic pollutants, but these methods are insufficient to remove chemically stable dyes that remain in the treated wastewater. However, the photocatalytic degradation process is an efficient approach to degrade the dye up to the maximum extent with improved efficiency. Therefore, in this work, a new class of two-dimensional (2D) transition metal carbide of Titanium Carbide (Ti 3 C 2 Tx) MXene material was used for the organic dyes degradation such as MB and RhB using a photocatalytic process. A layered structure of hexagonal lattice symmetry of Ti 3 C 2 Tx MXene was successfully synthesized from the Titanium Aluminum Carbide of Ti 3 AlC 2 bulk phase using an exfoliation process. Further, the XRD spectrum confirms the transformation of bulk MAX phase having (002) plane at 9.2° to Ti 3 C 2 Tx MXene of (002) plane at 8.88° confirms the successful removal of Al layer from MAX phase. A smooth, transparent, thin sheet-like morphology of Ti 3 C 2 Tx nanosheet size were found to be in the range of 70 to 150 nm evaluated from TEM images. Also, no holes or damages in the thin sheets were found after the treatment with strong hydrofluoric acid confirms the formation Ti 3 C 2 Tx layered sheets. The synthesized Ti 3 C 2 Tx MXene possesses excellent photocatalytic activity for the degradation of dyes MB, RhB, and mixtures of MB and RhB dyes. MB dye degraded with a degradation percentage efficiency of 99.32% in 30 min, while RhB dye was degraded upto 98.9% in 30 min. Also, experiments were conducted for degradation of mixture of MB and RhB dyes by UV light, and the degradation percentage efficiency were found to be 98.9% and 99.75% for mixture of MB and RhB dye in 45 min, respectively. Moreover, reaction rate constant ( k ) was determined for each dye of MB, RhB, and mixtures of MB and RhB and was found to be 0.0215 min −1 and 0.0058 min −1 , and for mixtures, it was 0.0020 min −1 and 0.009 min −1 , respectively.

Most of the studies focused on V2O5 have been devoted to obtaining specific morphology and microstructure for its intended applications. Two dimensional (2D) V2O5 has the most valuable structure because of its unique planar configuration that can offer more active sites. In this study, a bottom-up and low-cost method that is hydrothermal combined with spin-coating and subsequent annealing was developed to prepare 2D V2O5 nanosheets film on quartz substrate. First, VOOH nanosheets were prepared by the hydrothermal method using V2O5 powders and EG as raw materials. Further, V2O5 nanosheets with an average lateral size over 500 nm and thickness less than 10 nm can be prepared from the parent VOOH nanosheets by annealing at 350 °C for 15 min in air. The prepared V2O5 nanosheets film was assembled of multiple nanosheets. The structural, morphological, microstructural and optical properties of the films were respective investigated by XRD, SEM, TEM and UV-Vis. The photodetector based on V2O5 nanosheets film shows good photoresponse with a response time of 2.4 s and a recovery time of 4.7 s.

Porous alumina with high specific surface area (SSA) and large pore volume (PV) is highly desired in various applications; however, its synthesis without an organic template faces a great challenge. Herein, we propose a novel template-free strategy based on intercalation-exfoliation with silica to weaken boehmite (alumina precursor) interlayer forces and achieve the exfoliation of boehmite into two-dimensional (2D) nanosheets, which can easily be scaled up. The as-prepared 2D nanosheets with 2-nm thickness could be assembled to form boehmite with 542 m 2 g −1 SSA and 2.43 cm 3 g −1 PV. The porous alumina obtained from the thermal/hydrothermal treatment of the 2D nanosheets at different temperatures possesses a hierarchical porous structure superior to most of the reported alumina synthesized with organic templates, exhibiting excellent performance in the adsorption of large organic molecules. This research provides a new strategy for synthesizing 2D boehmite nanosheets and porous alumina materials, demonstrating great potential in catalysis and adsorption.

Nanoparticle photosensitizers possess technical advantages for photocatalytic reactions due to enhanced light harvesting and efficient charge transport. Here we report synthesis of semiconductor nanoparticles through covalent coupling and assembly of metalloporphyrin with condensed carbon nitride. The resultant nanoparticles consist of light harvesting component from the condensed carbon nitride and photocatalytic sites from the metalloporphyrins. This synergetic particle system effectively initiates efficient charge separation and transport and exhibits excellent photocatalytic activity for CO 2 reduction. The CO production rate can reach up to 57 µmol/(gh) with a selectivity of 79% over competing H 2 evolution. Controlled experiments demonstrate that the combination of light harvesting with photocatalytic activity via covalent assembly is crucial for the high photocatalytic activity. Due to effective charge separation and transfer, the resultant nanoparticle photocatalysts show exceptional photo stability against photo-corrosion under light irradiation, enabling for long-term utilization. This research opens a new way for the development of stable, effective nanoparticle photocatalysts using naturally abundant porphyrin pigments.