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Template-Free Synthesis of Zn<sub>1β<i>x</i></sub>Cd<sub><i>x</i></sub>S Nanocrystals with Tunable Band Structure for Efficient Water Splitting and Reduction of Nitroaromatics in Water
A facile, one-pot,
solvothermal synthesis of nanocrystals (NCs)
of Zn<sub>1β<i>x</i></sub>Cd<sub><i>x</i></sub>S (<i>x</i> = 0.1 (<b>S1</b>)β0.9 (<b>S9</b>)) solid solutions has been successfully carried out using
4,4β²-dipyridyldisulfide (DPDS = (C<sub>5</sub>H<sub>4</sub>N)<sub>2</sub>S<sub>2</sub>)) as a new temperature-dependent <i>in situ</i> source of S<sup>2β</sup> ions. Powder XRD
patterns of the samples revealed gradual phase transformation from
cubic to hexagonal upon increasing the Cd content (<i>x</i>) in the solid solutions Zn<sub>1β<i>x</i></sub>Cd<sub><i>x</i></sub>S (0 β€ <i>x</i> β€
1). FESEM analyses showed almost spherical morphology of the solid
solutions, <b>S2</b>, <b>S5</b>, and <b>S9</b>.
HR-TEM analyses of <b>S3</b> and <b>S9</b> unveiled the
presence of small nanocrystals (NCs) of size 7 and 15 nm, respectively,
and highlights the discontinuity in the pattern of lattice fringes.
Optical measurements revealed that Zn<sub>1β<i>x</i></sub>Cd<sub><i>x</i></sub>S solid solutions exhibit precisely
tunable band structure with varying the concentration of Cd content.
Furthermore, visible-light-assisted photocatalytic investigation revealed
very good activity of the Zn<sub>0.7</sub>Cd<sub>0.3</sub>S solid
solution for water splitting with H<sub>2</sub> generation rate of
750 ΞΌmol h<sup>β1</sup> g<sup>β1</sup>. Interestingly,
for the first time, the water splitting activity of the Zn<sub>1β<i>x</i></sub>Cd<sub><i>x</i></sub>S NCs has been applied
for efficient reduction of nitroaromatic pollutants in water by utilizing
water as a source of hydrogen. Remarkably, various substituted nitroaromatics
containing both electron-donating and -withdrawing groups as well
as dinitroaromatics can be efficiently reduced to their corresponding
amines in high yield and selectivity. Also, the photocatalyst can
be recycled and reused for several cycles without significant loss
of the activity. The plausible mechanism for the reduction of nitroaromatics
in water by Zn<sub>1β<i>x</i></sub>Cd<sub><i>x</i></sub>S solid solution has also been studied. Herein we
demonstrate a unique approach wherein water acts as a source of reducing
agent for the visible-light-assisted photocatalytic reduction of nitroaromatic
pollutants in water by Zn<sub>1β<i>x</i></sub>Cd<sub><i>x</i></sub>S solid solutions