Phosphorus-doped hexagonal tubular carbon nitride (P-TCN) with the layered stacking structure was obtained from a hexagonal rod-like single crystal supramolecular precursor (monoclinic, C2/m). The production process of P-TCN involves two steps: 1) the precursor was prepared by self-assembly of melamine with cyanuric acid from in situ hydrolysis of melamine under phosphorous acid-assisted hydrothermal conditions; 2) the pyrolysis was initiated at the center of precursor under heating, thus giving the hexagonal P-TCN. The tubular structure favors the enhancement of light scattering and active sites. Meanwhile, the introduction of phosphorus leads to a narrow band gap and increased electric conductivity. Thus, the P-TCN exhibited a high hydrogen evolution rate of 67 μmol h(-1) (0.1 g catalyst, λ >420 nm) in the presence of sacrificial agents, and an apparent quantum efficiency of 5.68 % at 420 nm, which is better than most of bulk g-C3 N4 reported.
Polymeric
carbon nitride (C3N4) has emerged
as the most promising candidate for metal-free photocatalysts but
is plagued by low activity due to the poor quantum efficiency and
low specific surface area. Exfoliation of bulk crystals into ultrathin
nanosheets has proven to be an effective and widely used strategy
for enabling high photocatalytic performances; however, this process
is complicated, time-consuming, and costly. Here, we report a simple
bottom-up method to synthesize porous few-layer C3N4, which involves molecule self-assembly into layered precursors,
alcohol molecules intercalation, and subsequent thermal-induced exfoliation
and polycondensation. The as-prepared few-layer C3N4 expose more active sites and greatly enhance the separation
of charge carriers, thus exhibiting a 26-fold higher hydrogen evolution
activity than bulk counterpart. Furthermore, we find that both the
high activity and selectivity for the oxidative coupling of amines
to imines can be obtained under visible light that surpass those of
other metal-free photocatalysts so far.
Establishing highly effective charge transfer channels in carbon nitride (C3N4) for enhancing its photocatalytic activity is still a challenging issue. Herein, for the first time, the engineering of C3N4 layers with single‐atom Cu bonded with compositional N (CuNx) is demonstrated to address this challenge. The CuNx is formed by intercalation of chlorophyll sodium copper salt into a melamine‐based supramolecular precursor followed by controlled pyrolysis. Two groups of CuNx are identified: in one group each of Cu atoms is bonded with three in‐plane N atoms, while in the other group each of Cu atoms is bonded with four N atoms of two neighboring C3N4 layers, thus forming both in‐plane and interlayer charge transfer channels. Importantly, ultrafast spectroscopy has further proved that CuNx can greatly improve in‐plane and interlayer separation/transfer of charge carriers and in turn boost the photocatalytic efficiency. Consequently, the catalyst exhibits a superior visible‐light photocatalytic hydrogen production rate (≈212 µmol h−1/0.02 g catalyst), 30 times higher than that of bulk C3N4. Moreover, it leads to an outstanding conversion rate (92.3%) and selectivity (99.9%) for the oxidation of benzene under visible light.
Thermally-stable, ordered mesoporous anatase TiO 2 with large pore size and high crystallinity has been successfully synthesized through an evaporationinduced self-assembly technique, combined with encircling ethylenediamine (EN) protectors to maintain the liquid crystal mesophase structure of TiO 2 primary particles, followed by calcination at higher temperature. The structures of the prepared mesoporous TiO 2 are characterized in detail by small-angle and wide-angle X-ray diffraction, Raman spectra, N 2 adsorption/ desorption isotherms, and transmission electron microscopy. Experimental results indicate that the well-ordered mesoporous structure could be maintained up to 700 ° C (M700) and also possesses large pore size (10 nm), high specifi c BET surface area (122 m 2 g − 1 ), and high total pore volumes (0.20 cm 3 g − 1 ), which is attributed to encircling EN protectors for maintaining the mesoporous framework against collapsing, inhibiting undesirable grain growth and phase transformation during the calcination process. A possible formation mechanism for the highly stable large-pore mesoporous anatase TiO 2 is also proposed here, which could be further confi rmed by TG/FT-IR in site analysis and X-ray photoelectron spectroscopy. The obtained mesoporous TiO 2 of M700 exhibit better photocatalytic activity than that of Degussa P25 TiO 2 for degradation of highly toxic 2,4-dichlorophenol under UV irradiation. This enhancement is attributed to the well-ordered large-pore mesoporous structure, which facilitates mass transport, the large surface area offering more active sites, and high crystallinity that favors the separation of photogenerated electron-hole pairs, confi rmed by surface photovoltage spectra.
Zinc oxide with excellent photocatalytic performance for the photodegradation of dyes (superior to Degussa P25 TiO(2)) could be easily prepared in large quantity by direct calcination of zinc acetate (Zn(Ac)(2)·2H(2)O).
Actiniae‐like carbon nitride (ACN) bundles were synthesized by the pyrolysis of an asymmetric supramolecular precursor prepared from L‐arginine (L‐Arg) and melamine. ACN has adjustable band gaps (2.25 eV–2.75 eV) and hollow microtubes with ultrathin pore walls, which enrich reaction sites, improve visible‐light absorption and enhance charge separation. In the presence of phenylcarbinol, ACN exhibited excellent water‐splitting ability (95.3 μmol h−1) and in the meanwhile phenylcarbinol was selectively oxidized to benzaldehyde (conversion of 90.9 %, selectivity of 99.7 %) under solar irradiation. For the concurrent reactions, 2D isotope labeling, separation, and detection were conducted to confirm that the proton source of released hydrogen is water. The mechanism of water splitting and phenylcarbinol oxidation was also investigated.
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