catalysts Article Optical Management of CQD/AgNP@SiNW Arrays with Highly Efficient Capability of Dye Degradation Po-Hsuan Hsiao 1 , Sasimontra Timjan 1 , Kuan-Yi Kuo 1 , Joon-Ching Juan 2 and Chia-Yun Chen 1,3, *   Citation: Hsiao, P.-H.; Timjan, S.; Kuo, K.-Y.; Juan, J.-C.; Chen, C.-Y. Optical Management of CQD/AgNP@SiNW Arrays with Highly Efficient Capability of Dye Degradation. Catalysts 2021, 11, 399. https://doi.org/10.3390/catal11030399 Academic Editor: Vincenzo Vaiano Received: 24 February 2021 Accepted: 18 March 2021 Published: 22 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Materials Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan; k811207416@gmail.com (P.-H.H.); sasimontra06@gmail.com (S.T.); kuanyi1115@gmail.com (K.-Y.K.) 2 Nanotechnology & Catalysis Research Centre, Institute for Advanced Studies, University of Malaya, Kuala Lumpur 50603, Malaysia; jcjuan@um.edu.my 3 Hierarchical Green-Energy Materials (Hi-GEM) Research Center, National Cheng Kung University, Tainan 70101, Taiwan * Correspondence: timcychen@mail.ncku.edu.tw; Tel.: +886-6-275-7575 (ext. 62952) Abstract: The facile synthetic method for the preparation of incorporated carbon quantum dots (CQDs)/Ag nanoparticles (AgNPs) with well-aligned silicon nanowire (SiNW) arrays is demon- strated, offering the superior photodegradation capabilities covering UV to visible wavelength regions. By examining the morphology, microstructure, crystallinity, chemical feature, surface groups, light-emitting, and reflection characteristics, these hybrid heterostructures are systematically identi- fied. Moreover, the involving degradation kinetics, band diagram, cycling capability, and underlying mechanism of photodegradation are investigated, validating their remarkable and reliable photocat- alytic performances contributed from the strongly reduced light reflectivity, superior capability of charge separation, and sound wettability with dye solutions. Keywords: carbon nanodots; silicon nanowires; heterostructure; photodegradation 1. Introduction Heterostructures, through the incorporation of distinct semiconductor and/or metal nanostructures, have emerged as the extensive investigations arisen from their innovative and superior optoelectronic [1,2], mechanic [3], and optical [4–7] properties, which further lead to the substantial improvement of various applications, ranging from photodetec- tors [8–11], solar cells [12–14], optical communications [15], to biological detection [16]. In the practical regard, nevertheless, the synthetic method of heterostructures turn out to be critical for attaining the requirement of manufacturing standards such as large production, simple procedure and sound reliability. Compared with the reported methods including chemical vapor deposition, physical evaporation, laser-induced deposition, hydrothermal, and in-situ nanoparticle synthesis [17–21], solution-processing techniques allow several superiorities, such as simple, inexpensive, and large-quantitative production of nanosized heterostructures [22], which are highly potential for addressing practical employment of commercial product. Yet, the correlated studies are still limited so far. In this study, all-solution based method is presented for the preparation of highly efficient photocatalysts through the strategy of heterostructure design. Organic dyes, one of the dominant water pollutants, cause the serious destruction to the ecosystems. Degradation of organic dyes using photocatalysts under light illuminations has been con- sidered the efficient and reliable treatment that can ecofriendly degrade the harmful dyes to CO 2 and water. To realize the broadband photocatalysts that can activate the dye degra- dation covering the wide spectral regions from ultraviolet (UV) to visible illuminations, optical management of heterostructures for accomplishing the efficient light absorption of both UV and visible wavelengths turns out to be critically essential. Herein, the well incorporation of Ag nanoparticles (AgNPs) as outer sides with carbon nanodots (CQDs) Catalysts 2021, 11, 399. https://doi.org/10.3390/catal11030399 https://www.mdpi.com/journal/catalysts