## 4 Conclusions  
ZnO was chosen as an alternative semiconductor to TiO\({}_{2}\) and doped with copper oxides to improve catalytic efficiency. However, the proposed catalysts, which were less efficient than CuO/TiO\({}_{2}\), required longer reaction times, which were hindered by the photodegradation of Cu\({}_{x}\)O. As a result, it was not possible to achieve outcomes comparable to those obtained with CuO/TiO\({}_{2}\). To address this, the catalyst was protected with a PDA shell to extend its lifespan, thus maintaining activity beyond 72 h of reaction. This allowed the catalyst to produce results comparable to the reference material. Furthermore, adding a co-catalytic amount of sodium ascorbate increased the reaction selectivity, achieving significantly higher yields and selectivities for SA compared to the TiO\({}_{2}\)-based reference system. Incorporating PDA as a protective shell represents a promising strategy to address the photodegradation of copper oxide-based catalysts. By leveraging sustainable materials and improving catalyst durability, this work contributes to the development of more environmentally friendly photocatalytic systems, able to produce SA from MA in water with catalytic sodium ascorbate amount under UV light. In this way, it was possible to  
Figure 4: Conversion and yields during aqueous MA photoreduction to SA employing Cu\({}_{2}\)O/ZnO-PDA as photocatalyst and sodium ascorbate as co-catalyst under 254 nm.  
Figure 5: Reaction scheme of MA conversion to FA and SA.  
obtain a SA yield of 61% with a selectivity of 67%. Studies on the reaction mechanism to have experimental evidence on the role of ascorbate will need to be conducted.  
The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app15031631/s1](https://www.mdpi.com/article/10.3390/app15031631/s1)]([https://www.mdpi.com/article/10.3390/app15031631/s1](https://www.mdpi.com/article/10.3390/app15031631/s1)), Figure S1: XRD pattern of CuO/ZnO (A) and Cu\({}_{2}\)O/ZnO-PDA (B); Figure S2: \({}^{1}\)HNMR photoreduction of MA carried out in H\({}_{2}\)O without any catalyst at 0 h reaction time; Figure S3: \({}^{1}\)HNMR photoreduction of MA carried out in H\({}_{2}\)O without any catalyst at 12 h reaction time; Figure S4: \({}^{1}\)HNMR photoreduction of MA carried out in H\({}_{2}\)O employing the catalyst Cu\({}_{2}\)O/ZnO-PDA with equimolar sodium ascorbate at 0 h reaction time; Figure S5: \({}^{1}\)HNMR photoreduction of MA carried out in H\({}_{2}\)O employing the catalyst Cu\({}_{2}\)O/ZnO-PDA with equimolare sodium ascorbate at 24 h reaction time; Figure S6: \({}^{1}\)HNMR photoreduction of MA carried out in H\({}_{2}\)O employing the catalyst Cu\({}_{2}\)O/ZnO-PDA with sodium ascorbate in co-catalytic amount at 48 h reaction time; Figure S10: \({}^{1}\)HNMR photoreduction of MA carried out in H\({}_{2}\)O employing the catalyst Cu\({}_{2}\)O/ZnO-PDA with sodium ascorbate in co-catalytic amount at 72 h reaction time; Figure S11: \({}^{1}\)HNMR photoreduction of MA carried out in D\({}_{2}\)O employing the catalyst Cu\({}_{2}\)O/ZnO-PDA with sodium ascorbate in co-catalytic amount at 24 h reaction time.  
Conceptualization, F.C. and L.T.; methodology, F.C.; investigation, F.C., A.M. and G.R.; data curation, F.C.; writing--original draft preparation, F.C. and A.M.; writing--review and editing, N.d. and L.T.; supervision, N.d. and L.T.; project administration, L.T.; funding acquisition, L.T. All authors have read and agreed to the published version of the manuscript.  
The research project was partially supported by the FSE-REACT-EU, PON Ricerca e innovazione 2014-2020 DM 1062/202, Cod: MUR 53-G-14753.  
Not applicable.  
The data are available upon request due to restrictions. The data presented in this study are available upon request from the corresponding author.  
The authors acknowledge the CAST--Center for Advanced Studies and Technology of Chieti for supplying the cryogenic gases.  
The authors declare no conflicts of interest.