| Due to their unique structure and physicochemical properties,two-dimensional nanomaterials attracted great attention in various fields,such as environmental adsorption,catalytic conversion o,organic contaminants,etc.The promising properties and applications promoted the rapid development of various synthetic methods,including mechanical/chemical exfoliation,chemical vapor deposition,templated synthesis,etc.However,it was still challenging to controllably fabricate two-dimensional nanomaterials using those top-down methods,e.g.,mechanical/chemical exfoliation,because of the limitations in high energy consumption,only applicable to layered bulk materials,etc.In contrast,those bottom-up methods,e.g.,templated synthesis and chemical vapor deposition,were more versatile in principle,and more powerful in controllability,which offered good choices for the preparation of two-dimensional nanomaterials.Nevertheless,all types of bottom-up methods were more dependent on the chemical reactions of certain precursors at proper and stable experimental conditions.The strong coupling forces from the non-layered two-dimensional nanomaterials also made it harder to control the orientation growth process,the final morphologies,and structures.To solve these issues,this work introduced space confinement into the templated synthesis of two-dimensional nanomaterials using a layered silicate RUB(Ruhr University Bochum)-15 as the template and nanoreactor.The reagents were confined due to the open two-dimensional channels and the presence of diverse active sites on the surface,followed by a confined reaction,thus realizing materials’ controllable growth through the kinetic process.The specific contents were as follows:(1)N-doped graphene-like carbon(NGLC)nanosheets were synthesized via a layered-confinement strategy by using RUB-15 as the template and dopamine as the precursor.Through the self-polymerization of dopamine and confined carbonization in the interlayer space of RUB-15,NGLC nanosheets were obtained.The final product presented a nanosheet structure with regular size.The stacked graphene-like layers could be observed clearly at the edge of NGLC nanosheets.Meanwhile,the NGLC was endowed with abundant surface-active groups and porous structures.The maximum adsorption capacities toward cationic dyes,rhodamine B(RhB)and methylene blue(MB),reached as high as 1272.74 mg·g-1 and 679.55 mg·g-1.respectively.indicating the promising potential for cationic contaminants removal.Besides,excellent reusability and wide pH suitability(2-10)were observed by batch adsorption experiments.The much better adsorption performance of NGLC than that of bulk polydopamine(PDA)carbon and carbon-based materials reported in recent years revealed the importance of the layered-confinement strategy.Further experiments confirmed that the excellent selectivity and promising adsorption performance resulted from the porous nanosheet structure and abundant surface-active groups.(2)Few-layer g-C3N4 nanosheets with nitrogen vacancies(NVs)were also synthesized via the RUB-15-based layered-confinement strategy by using cyanamide as the precursor.Through the in-suit pyrocondensation of cyanamide in the interlayer space of RUB-15,few-layer g-C3N4 nanosheets were obtained.The final product presented a few-layer nanosheet structure with a size range of 1.4 nm in thickness,which was well in agreement with the layer spacing of RUB-15,The optimization of structure expressed a positive effect on the catalytic performance.Few-layer g-C3N4 nanosheet showed a significantly higher(23.25-fold)bisphenol A(BPA)degradation rate of 3.162 h-1 than that of the bulk g-C3N4(B-C3N4)under visible light irradiation.As compared with many advanced g-C3N4-based photocatalysts reported in recent years,the photocatalytic performance of our material was competitive.Meanwhile,the few-layer g-C3N4 nanosheet had good recyclability and excellent degradation performances toward different types of organic contaminants(phenolic compounds,antibiotics,etc.)under visible light irradiation.Further characterizations showed that the enhanced photocatalytic activity was assigned to the few-layer nanosheet structure and the introduction of NVs.The density functional theory(DFT)calculations demonstrated that the introduction of NVs and g-C3N4 structure optimizing resulted in the lowering of bandgap energy,increased active sites,and stronger photo-adsorption ability.Besides,the few-layer structure with abundant pores endowed the catalyst larger surface area and abundant channels,which facilitated the kinetics of the photocatalytic reaction with faster mass transfer.(3)Fe@g-C3N4 catalyst with high-density Fe sites and g-C3N4 nanosheet was prepared by the in-suit pyrocondensation of cyanamide and Fe precursors in argon.Through the mixed intercalation of Fe precursors and cyanamide,and following a confined pyrocondensation process,Fe@g-C3N4 nanosheets were obtained.Such a method solved problems of Fe species aggregation during the preparation process for the classical approach.The final product presented a two-dimensional nanosheet structure.Fe species were dispersed in g-C3N4 in the form of Fe-Nx coordination compound and ultra-small nanoparticles.Fe-based Fenton catalysis and g-C3N4-based photocatalysis work together to promote catalytic degradation efficiency.When applied in the photo-Fenton catalytic degradation of BPA,almost BPA was oxidized by the Fe@g-C3N4 nanosheet in 10 min.The catalytic activity was 4.53-fold and 99.31-fold higher than those of bulk Fe@g-C3N4 catalyst(Fe@g-C3N4-B)and substrate material g-C3N4-Ar,respectively.Meanwhile,the Fe@g-C3N4 nanosheet had good recyclability and stability.The enhanced catalytic activity was assigned to the two-dimensional nanosheet structure and high-density Fe sites.(4)The Au-SnO2/SiO2 catalyst was obtained by using RUB-15 as the substrate material and nanoreactor.With the aid of the ion exchange and Sn(Ⅱ)-assisted in situ reduction process,homogeneously dispersed Au-SnO2 nanoparticles(NPs)(3.23±0.85 nm)were generated in the confined layer space of RUB-15.The interlayer space of the catalyst was innovatively used as a confined reaction space in the reduction of 4-nitrophenol(4-NP),the Au-SnO2/SiO2 composite showed excellent catalytic activity with a rate constant of 6.64 min-1 at room temperature,which was dramatically higher than that of the Au/SiO2 composite produced by reduction with hydrazine hydrate on the same support of layered silicate RUB-15.The superior catalytic activity of the Au-SnO2/SiO2 composite was attributed to the following aspects:(1)the nanosheet structure with high surface area and high dispersion of Au-SnO2 NPs exposed more active sites;(2)the layered support provided effective and tight protection for actives sites against harsh reaction medium;(3)the interaction between Au and SnO2 NPs promoted the electron transfer from BH4-to Au NPs,thus synergistically optimized both the electron density around Au NPs and adsorption energy of 4-aminophenol(4-AP)on Au NPs,and thus improve the reaction kinetics.In summary,a RUB-15-based layered-confinement strategy was developed for the controlled synthesis of two-dimensional nanomaterials.The successful fabrication of a series of two-dimensional nanomaterials,including the NGLC nanosheets,few-layer g-C3N4 nanosheets.Fe@g-C3N4 nanosheets,and Au-SnO2/SiO2 composite,demonstrated that the layered-confinement synthesis via RUB-15 was adaptable.The precursor type,concentration-etc.,were precisely controlled for tuning the epitaxial growth process,shape,and size.The superior performances of these two-dimensional nanomaterials in fields of environmental adsorption,and catalytic conversion indicated the great advantages of the RUB-15-based layered-confinement strategy for the fabrication of high-performance adsorbent/catalysts.Combining experiments,characterizations,and theoretical calculations,the correlation between the nanosheet structure and performance was studied thoroughly.This work paved a rational pathway for the fabrication of functionalized nanomaterials via a layered-confinement strategy. |
