Orange Zn–Al–O–N Powder Active for Photocatalytic Water Reduction and Oxidation Synthesized from a Zn–Al Layered Double Hydroxide Using Urea as the Nitriding Agent

Abstract

The development of colored inorganic powders that are inexpensive, chemically stable, and nontoxic is important for applications such as heterogeneous photocatalysts and pigments. Here, we show that a ZnO-based orange powder can be synthesized through thermal conversion of a two-dimensional Zn−Al layered double hydroxide (LDH) in the presence of urea as a nitriding agent, thereby avoiding the use of expensive, poisonous NH 3 gas. Heating a mixture of Zn−Al LDH and urea under a flow of N 2 at 773 K yielded N-doped ZnO as the main crystalline phase, along with a small amount of Zn(CN 2 ). At temperatures greater than 873 K, N-doped ZnO with deep-orange coloration began to appear as the main phase, accompanied by a small amount of γ-AlON. The orange color, which was attributed to the formation of a N-doped ZnO phase, became more prominent with increasing temperature up to 973 K. At temperatures greater than 973 K, an optically transparent ZnAl 2 O 4 phase was dominant, resulting in a loss of the orange coloration. Nitridation of Zn 5 (OH) 6 (CO 3 ) 2 and γ-AlOOH, which are analogous layered compounds prepared in a manner similar to that of Zn−Al LDH, with urea at 973 K did not yield an orange product. Under visible light, the Zn−Al−O−N powder produced H 2 from aqueous methanol solution and O 2 gas from a silver nitrate solution, with apparent quantum yields of 0.26 and 1.8% at 420 nm, respectively. This work highlights that the use of base metal-based LDH and an inexpensive solid nitrogen source may provide a unique platform for synthesizing a new photocatalyst material, which is unattainable with the previous method using toxic ammonia gas.

Soil-mimetic eco-friendly fertilizer gates: nanoclay-reinforced binary carbohydrates for improving crop efficiency

“…1d). 47 Finally, after the addition of lignin, the shoulder peaks were retained that may also include the additional coordination of Al 3+ with –OH groups in lignin (Fig. 1e), which ensures the strong inter-component binding between the coating materials.…”

“…Here, the appearance of a Si peak was assigned to the silicon wafer substrate used for the sample preparation. The XRD analysis of the NC (JCPDS 38-0486) 47 exhibits a rhombohedral crystal phase and an R 3̄ m space group with the characteristic 2 θ peaks at 11.7° and 23.4° that correspond to the (003) and (006) planes from basal spacings of 0.75 nm and 0.38 nm, respectively, (Fig. 1c).…”