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Journal ArticleDOI

Photocatalytic reduction of dinitrogen to ammonia over noble-metal-loaded TiO2

TL;DR: The photocatalytic reduction of dinitrogen to ammonia is influenced by the nature and amount of metal loading on TiO2 and the optimum metal content varies depending on the nature of the metal as mentioned in this paper.
Abstract: The photocatalytic reduction of dinitrogen to ammonia is influenced by the nature and amount of metal loading on TiO2. The optimum metal content varies depending on the nature of the metal. A correlation between the ammonia yield and the intermediary MH bond strength is established (low bond strength gives rise to low ammonia yield).
Citations
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Journal ArticleDOI
TL;DR: In this article, B atoms and cyano groups co-doped graphite carbon nitride with nitrogen vacancies (VN-BC-CN) via one-step in-situ route.

26 citations

Journal ArticleDOI
TL;DR: In this paper, the electrostatic self-assembly method was used to synthesize supported Pt-TiO photocatalysts on carbonaceous supports to study CO photoreduction to produce CH₄.

26 citations

Journal ArticleDOI
01 Feb 2021
TL;DR: In this article, the recent development in the fundamental understanding of photocatalytic NH3 synthesis and the methods of precise NH3 detection are summarized, and the strategy for surface engineering and interface engineering of photocATalysts toward photocatalyst-enhanced NH3 production has been thoroughly analyzed with the aim to stimulate critical thinking about the effective methodology for catalyst modification instead of exploring new materials.
Abstract: Photocatalytic ammonia (NH3) synthesis from N2 and water driven by solar energy is a sustainable and environmentally friendly technology, which has gained considerable attention in recent years. In this review, the recent development in the fundamental understanding of photocatalytic NH3 synthesis and the methods of precise NH3 detection are summarized. More importantly the strategy for surface engineering and interface engineering of photocatalysts toward photocatalytic NH3 production has been thoroughly analyzed with the aim to stimulate critical thinking about the effective methodology for catalyst modification instead of exploring new materials. At the end the challenges and a few concerns are raised from the current reports and future perspectives in this research field are discussed targeting to clarify the reliability and reproducibility of the photochemical process and to direct the future research direction, such as flow reactor design and in-depth understanding of the underlying reaction pathway.

26 citations

Journal ArticleDOI
TL;DR: Density functional theory (DFT) simulations show that lithium doping can not only increase the N[triple bond, length as m-dash]N bond length, which activates N2 molecules, but also promote the electron-hole separation efficiency of g-C3N4.
Abstract: In this work, three-dimensional macroporous lithium doped graphitic carbon nitride was synthesized. XRD, N2 adsorption, SEM, XPS, UV-Vis spectroscopy, N2-TPD and photoluminescence were used to characterize the prepared catalysts. The result shows that lithium exists as a coordinative Li–N bond, which can chemisorb and activate N2 molecules, and promote the electron transfer from the catalyst to the nitrogen molecules. The as-prepared lithium doped g-C3N4 shows a NH4+ production rate of 4.8 mg L−1 h−1 gcat−1, which is 20 times that of bulk g-C3N4. Density functional theory (DFT) simulations show that lithium doping can not only increase the NN bond length, which activates N2 molecules, but also promote the electron–hole separation efficiency of g-C3N4.

23 citations

Journal ArticleDOI
TL;DR: In this paper, a carbon self-doped honeycomb-like g-C3N4 with outstanding N2 photofixation ability was prepared via microwave treatment, and the synergy effect of carbon doping and microwave treatment also enhances the surface area and separation efficiency of electron-hole pairs.
Abstract: Light harvesting is an important part of the photocatalysis process. In this work, carbon self-doped honeycomb-like g-C3N4 with outstanding N2 photofixation ability was prepared via microwave treatment. XRD, N2 adsorption, UV-Vis, SEM, XPS, ESR and PL were used to characterize the as-prepared catalysts. Combining the carbon self-doping with microwave treatment, the n–π* transition was successfully stimulated. The remarkable red shift of absorption edge from 465 nm to near 600 nm was observed, leading to the obviously promoted visible light absorption. The synergy effect of carbon doping and microwave treatment also enhances the surface area and separation efficiency of electron–hole pairs. The as-prepared catalyst displays the highest NH4+ concentration of 5.3 mg L−1 gcat−1, over 11 times higher than that of neat g-C3N4, as well as excellent photocatalytic stability. DFT calculation was also used to further prove our point of view. This paper provides a new way for the construction of high efficiency photocatalysts.

22 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the dependence of the exchange current for the electrolytic evolution of hydrogen on metals (i 0,H ) on the work function is analyzed on the basic of a new list of polycrystalline surfaces.

1,474 citations

Journal ArticleDOI
TL;DR: The photolysis of chemisorbed water on incompletely outgassed TiO/sub 2/ powder yields H 2 and O 2 in the molar ratio of 2 : 1 if conducted under argon in the presence of molecular nitrogen as mentioned in this paper.
Abstract: The photolysis of chemisorbed water on incompletely outgassed TiO/sub 2/ powder yields H/sub 2/ and O/sub 2/ in the molar ratio of 2 : 1 if conducted under argon In the presence of molecular nitrogen, O/sub 2/ is still formed but the evolution of H/sub 2/ is inhibited as chemisorbed nitrogen is reduced to NH/sub 3/ and traces of N/sub 2/H/sub 4/ according to N/sub 2/ + 3H/sub 2/O + nhv yields 2NH/sub 3/ + 150/sub 2/ and N/sub 2/ + 2H/sub 2/O + mhv yields N/sub 2/H/sub 4/ + O/sub 2/ Iron doping enhances the photocatalytic reactivity of rutile and provides prototypes of solar cells for photochemical ammonia synthesis from N/sub 2/ and H/sub 2/O

817 citations

Journal ArticleDOI
TL;DR: In this article, the improvement of H/sub 2/ evolution from two different types of catalytic p-type photocathode surfaces has been examined, and a comparison of the naked p-Si, the simply platinized, and the (PQ/sup 2 +//sup ///sup +/.)sub n/.nPt(0))/sub surf/ system compared to the same surface directly platinised confirm an important difference in the mechanism of H /sub 2 / evolution catalysis for the two surface catalyst systems.
Abstract: The improvement of H/sub 2/ evolution from two different types of catalytic p-type photocathode surfaces has been examined. p-Type Si has been platinized by phtotelectrochemically plating Pt(0) onto the Si surface. Such a photocathode shows significant improvement (compared to naked p-type Si) for photochemical H/sub 2/ evolution with respect to output photovoltage, fill factor, and overall efficiency. Such photocathodes having an optimun amount of Pt(0) give a pH-dependent output voltage with respect to the H/sub 2/O/H/sub 2/ couple, but the dependence is not a simple 59-mV/pH dependence. No pH dependence would be expected if Pt(0) formed a Schottky barrier when plated onto p-type Si. A second kind of H/sub 2/ evolution catalyst has been confined to the surface of p-type Si. Polymeric quantities of an electroactive N,N'-dialkyl-4,4'-bipridinium reagent, (PQ/sup 2 +/.)/sub n/, have been confined to the surface. The Br/sup -/ counterions of the polymer are then exchanged by PtCl/sub 6//sup 2 -/. Photoreduction then yields Pt(0) dispersed in the polymer. Such a surface is again significantly improved compared to naked p-type Si with respect to H/sub 2/ evolution. A comparison of the naked p-Si, the simply platinized, and the (PQ/sup 2 +//sup ///sup +//sub n/.nPt(0))/sub surf./ system is mademore » and contrasted to the expected behavior of an external Schottky barrier photocell driving an electrolysis cell with a Pt cathode. Experiments with n-type MoS/sub 2/, n-type Si, Pt, Au, and W cathodes functionalized with the (PQ/sup 2 +//sup ///sup +/.)sub n/.nPt(0))/sub surf./ system compared to the same surface directly platinized confirm an important difference in the mechanism of H/sub 2/ evolution catalysis for the two surface catalyst systems. p-Type Si modified with optimum amounts of Pt(0) by direct platinization appears to give improved H/sub 2/ evolution efficiency by a mechanism where the Pt(0) serves as a catalyst that does not alter the interface energetics of the semiconductor.« less

318 citations

Journal ArticleDOI
TL;DR: The quantum yield of hydrogen production was increased greatly by supporting metals or metal complexes on the TiO2 surface, amounting to 38% for a Pt-TiO2 photocatalyst.

218 citations

Journal ArticleDOI
TL;DR: In this paper, the Fermi level difference of p-InP and H/sup +//H/sub 2/ (0.9 +/- 0.2 eV) was shown to be a function of metal work functions.
Abstract: Noble metal incorporation in the surface of p-type semiconductor photocathodes to catalyze hydrogen evolution leads to efficient solar to chemical conversion if a set of energetic and kinetic criteria are satisfied: (1) the semiconductor-catalyst junction barrier height must be equal to or greater than that of the semiconductor H/sup +//H/sub 2/ junction; (2) the recombination velocity of photogenerated electrons at the semiconductor-catalyst interface must be low; (3) the overpotential for hydrogen evolution at solar cell current densities (approx.30 mA/cm/sup 2/) must be minor. Because of substantial differences in the vacuum work functions of Pt, Rh, Ru, and the (redox potential of the) H/sup +//H/sub 2/ couple, the barrier heights for junctions of each of the four systems with p-InP ought to vary widely. Yet experiments show that all p-InP(M)/H/sup +//H/sub 2/ junctions, where M = Pt, Rh, Ru, or no metal, have essentially the same approx.0.7-V gain in onset potential for hydrogen evolution relative to Pt/H/sup +//H/sub 2/. We attribute the similarity to the known lowering of metal work functions upon hydrogen alloying. Such alloying increases the barrier height and thereby the gain in onset potential over that anticipated from the vacuum work functions. The barrier height, measured as themore » limiting value of onset potential gain at high irradiance, approaches in all cases the Fermi level difference of p-InP and H/sup +//H/sub 2/ (0.9 +/- 0.2 eV). That Fermi level pinning by interfacial states is not the cause of the similar barriers is evident from the reversible decrease in onset potential with hydrogen depletion and by a unity diode perfection factor of the p-InP(Rh)/H/sup +//H/sub 2/ photocathode, which indicates no measurable interfacial recombination of photogenerated carriers. In agreement, the quantum efficiency of carrier collection (hydrogen evolution) nears unity.« less

184 citations