Research On Design,Preparation And Photocatalytic Performance Of Two-Dimension Nano Materials Based Photocatalysts

Searching for efficient projects to deal with environmental pollution and energy shortage is one of great global challenge in this world.Solar energy,as one of clean and renewable energy source,has developed rapidly in recent years and been regarded as a promise future energy source.Among various environmental or renewable energy projects,solar energy-driven semiconductor based photocatalysis has been considered as a feasible project,and has gained interdisciplinary attention for its great potential in environmental and energy applications.As a key factor of photocatlysis,designing photocatalysts with high performance is the research hotspot in the field of photocatalysis.In recent years,two-dimensional semiconductor-based photocatalytic materials,such as metal-free organic polymer and transition metal dichalcogenides,expanded the design of photocatalysts because of their unique physical and chemical properties.This paper basing on the merits and contraposing the demerits of graphitic carbon nitride(g-C3N4)and tungsten disulfide(WS2),developed studies about design and preparation of high active two-dimension nano semiconductor-based photocatalysts and explored their applications in photocatalytic environmental remediation or solar energy to H2 conversion.Details are as follows:(1)Porous g-C3N4 nanosheets(U-g-C3N4)were successfully prepared via a direct heat treatment process by controlling the thermal condensation temperature of low-cost urea precursor.An excellent linear relation between the yield of U-g-C3N4 and the input urea was experimentally demonstrated,and consequently,a large-scale yield>50 g in a batch was readily achieved.Such a good linear relation could be use to achieve controllable yield of U-g-C3N4 by simply adjusting the amount of urea initially added in the reaction system.A series of characterizations revealed the actual evolutionary process of the temperature-dependent porous nanosheet architecture of U-g-C3N4.The results exhibited that 600 ? was the optimal temperature for the formation of g-C3N4 with porous nanosheet structure,and the as-prepared U-g-C3N4 possessed surface area of 88.7 m2/g and average pore diameter of 15.7 nm.Photocatalytic experiments demonstrated the extraordinary visible-light-driven photodegradation activity of U-g-C3N4 toward organic pollutants such as rhodamine B,safranine T,and ?-naphthol,and the excellent long-term photocatalytic degradation stability and reusability.Mechanism analysis revealed that the visible-light irradiation could induce the generation of ·O2?with high oxidation activity in the presence of U-g-C3N4,thus resulting in the degradation of organic pollutants.Such superior photodegradation performance and long-term photocatalytic stability,together with a scalable preparation method,may render U-g-C3N4 as a promising candidate for practical application in environmental remediation.(2)Fragmented P-doped g-C3N4 nanoflakes(PCNNFs),which were prepared by a two-step processing combining P-doping and nanostructure tailoring,were reported.Particularly,PCNNFs exhibited narrowed sub-bandgap from valence band to the midgap states and showed broad Urbach tail,extending light absorption region up to 800 nm.The resultant PCNNFs sample showed an enlarged surface area of 223.2 m2 g-1.The fragmented nanoflakes structure rendered PCNNFs much shortened charge-to-surface migration distance in both vertical-plane and in-plane direction.Such PCNNFs were demonstrated to be highly efficient in charge transfer and separation.Attributed to the synergistic effect of P-doping and fragmented nanoflakes structure,PCNNFs exhibited a remarkable visible-light(>420 nm)photocatalytic H2 production rate of 15921 ?molh-1 g-1 and quantum efficiencies of 6.74%at 420 nm and 0.24%at 600 nm.Moreover,even under long wavelength light(>470 nm),PCNNFs still exhibited high H2 production rate of 9546 ?molh-1 g-1,over 62 times the rate of pure g-C3N4.Prolonged photocatalytic experiments demonstrated the robustness of PCNNFs,and the PCNNFs sample showed no obvious changes in the crystalline structure and morphology after the prolonged photocatalytic H2 production experiment,confirming the good stability of PCNNFs.This work took multiple factors(i.e.surface area,light absoption,charge transfer and separation)into consideration,and successfully developed PCNNFs photocatalyst with enormously increased photocatalytic H2 production performance by combining doping and nanostructure tailoring.Such a work provided new strategy and insight for desgining and preparing highly active g-C3N4 based photocatalyst.(3)Manganese oxide(MnOx)decorated WS2 nanosheets(MnOx/WS2)hybrid photocatalyst was prepared by a photo-deposition process.A series of characterizations revealed that a small amount(?1 at.%)of MnOx decoration could render MnOx/WS2 more negative flat band potential,larger charge carrier density,lower impedance and higher photocurrent response comparing with pure WS2 nanosheets.These features were beneficial to the charge transfer and separation of MnOx/WS2 nanosheets,and thus rendered the MnOx/WS2 composite markedly enhanced visible-light-driven photocatalytic and photoelectrocatalytic activity.Furthermore,the hole-trapping function of MnOx in promoting efficient charge separation of WS2 nanosheets,which consequently boosted the photocatalytic activity,was experimentally investigated.This work based on the light absorption advantage of narrow bandgap WS2 and focused on improving the separation of photo-induced electron-hole pairs for improving photocatalytic activity,promoting a new route for the development of highly efficient photocatalysts.(4)Low-cost metallic-phase MoS2(M-MoS2)nanosheets were adopted to replace platinum as cocatalyst to assist PCNNFs for improving the performance of photocatalytic H2 production under visible light.M-MoS2 nanosheets prepared by a facile hydrothermal process were composited with PCNNFs by a simple physical mixing method,obtaining M-MoS2/PCNNFs composite photocatalyst.A series of characterizations comfirmed the characteristic metallic-phase of the as-prepared M-MoS2 nanosheets,and revealed that M-MoS2 nanosheets possessed good dispersibility and spreadability,and did not appear to exhibit bulk aggregation.By virtue of the advantages of metallic-phase,good dispersibility and spreadability,M-MoS2 nanosheets could well attach to PCNNFs,forming nice interface contact,thus achieving better performance as cocatalyst as well as facilitating separation of charge carriers.Consequently,M-MoS2/PCNNFs exhibited a markedly improved visible-light-driven photoctalytic H2 prodcution rate of 2450.9 ?mol h-1 g-1 without using platinum as cocatalyst,which was two orders of magnitude higher than that of PCNNFs under the same conditions.This work successfully developed an M-MoS2/PCNNFs photocatalyst with efficient photoctalytic H2 prodcution performance without using platinum as cocatalyst,promoting a new route for the development of highly efficient,low-cost and noble metal-free photocatalysts.