*3.3. Scavenging Experiments*

The contribution of hydroxyl radicals (HO• ), superoxide anion radicals (O<sup>2</sup> •−), and positive holes (h<sup>+</sup> ) in the degradation mechanism was evaluated using well-known scavengers, i.e., isopropanol (0.1M), p-benzoquinone (0.2mM), and methanol (0.1M), respectively [13].

## *3.4. Analytical Methods*

The concentration of amisulpride was quantified by a Dionex (Thermo Scientific) Ultimate 3000 UHPLC using an Acclaim™ RSLC 120 C18 (2.2 µm, 2.1 × 100 mm) column (Thermo Scientific) and an Acquity UPLC BEH C18 VanGuard™ pre-column (1.7 µm, 2.1 × 5 mm) from Waters. The mobile phase was a mixture of ultrapure water with 0.1% formic acid (80%) and acetonitrile (20%) with a flow rate of 0.15 mL min−<sup>1</sup> . The detection was performed at pollutant's λmax.

#### *3.5. UHPLC/MS Analysis*

TPs were identified by a UHPLC/MS system (Ultimate 3000 RSLC System (Thermo Scientific)/amaZon SL ion trap mass spectrometer from Bruker with an ESI source). A full description of the analysis is reported in our previous work [13]. For the determination of small-molecules TPs (carboxylic acids) that can be generated after the decay of the firststage TPs in heterogeneous photocatalysis, a Dionex P680 HPLC equipped with a Dionex PDA-100 Photodiode Array Detector and a Themo Scientific AQUASIL C18 (250 mm length <sup>×</sup> 4.6 mm ID <sup>×</sup> <sup>5</sup> <sup>µ</sup>m particle size) analytical column with a flow rate of 1 mL min−<sup>1</sup> was used. The mobile phase consisted of 1% acetonitrile and 99% 0.05 M KH2PO4, pH 2.8. The detection was performed at 210 nm.

## *3.6. Algal Biotest*

Algal bioassays were conducted using *Chlorococcum* sp. (strain SAG 22.83) and *Dunaliella tertiolecta* (CCAP19/6B) according to OECD 201 protocol [35], under sterile conditions and continuous illumination (4300 lux). BG-11 and F/2 were used as culture mediums for fresh and saltwater algal strains, respectively. The experiments were initiated by appropriate transfers of stock algal cultures to conical flasks containing the appropriate medium to maintain a supply of cells (1 <sup>×</sup> <sup>10</sup><sup>4</sup> cells mL−<sup>1</sup> ) in the logarithmic growth phase (final volume 100 mL). The samples collected at different stages were tested in duplicate cultures for 72 h with continuous stirring under the abovementioned conditions. The cell numbers were determined by using a Neubauer hemocytometer. Thereafter, the growth rate (µ) and the % inhibition of growth rate were calculated. The results are expressed as the mean ± SD.

#### **4. Conclusions**

The photocatalytic degradation of the pharmaceutical amisulpride was studied in UW and treated WW using UV-A irradiation and g-C3N<sup>4</sup> as the photocatalyst. High removal percentages were observed in both matrices. However, a slower degradation rate was ob-

served in WW that could be attributed to its complex composition containing both inorganic and organic substances. A scavenging study proved the significant contribution of h<sup>+</sup> and O<sup>2</sup> •− in the reaction mechanism. Oxidation, dealkylation, and cleavage of methoxy group were found to take place during the photocatalytic degradation of the studied pharmaceutical. Low inhibition in the growth rates and consequently low toxicity were observed at the beginning and during the photocatalytic process when UW was used as matrix, using microalgae *Chlorococcum* sp. and *Dunaliella tertiolecta.* In contrast, higher adverse effects were observed when WW was used as matrix. However, an overall abatement of the effects was noticed at 180 min. Based on the results, heterogeneous photocatalysis using g-C3N<sup>4</sup> showed good performance for the removal of amisulpride without the formation of harmful TPs. Considering that g-C3N<sup>4</sup> has a response to visible light and consequently solar light can be used for its activation, heterogeneous photocatalysis using g-C3N<sup>4</sup> is considered to be a promising method for removal of pharmaceuticals after the efficient separation of the photocatalyst or its immobilization on appropriate supports.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/catal13020226/s1, Figure S1: UV-Vis spectrum of amisulpride ([amisulpride]<sup>0</sup> = 1 mg L−<sup>1</sup> ); Figure S2: Effect of metal ions on the photocatalytic degradation of amisulpride in UW ([amisulpride]<sup>0</sup> = 1 mg L−<sup>1</sup> , [metal ion]<sup>0</sup> = 10 mg L−<sup>1</sup> , [g-C3N<sup>4</sup> ] = 300 mg L−<sup>1</sup> ); Figure S3: Effect of pH on the photocatalytic degradation of amisulpride in WW ([amisulpride]<sup>0</sup> = 1 mg L−<sup>1</sup> , [g-C3N<sup>4</sup> ] = 300 mg L−<sup>1</sup> ).

**Author Contributions:** Conceptualization, M.A.; methodology M.A., I.K. and I.R.; validation M.A.; formal analysis M.A.; investigation M.A., M.P., I.K. and I.R.; resources M.A.; data curation, M.A.; writing—original draft M.A. and I.R.; writing—review and editing M.A. and I.K.; visualization M.A.; supervision M.A; project administration M.A.; funding acquisition M.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This paper has been financed by the funding program "MEDICUS", of the University of Patras (Number: 81654).

**Data Availability Statement:** Data are contained within the article.

**Acknowledgments:** This paper has been financed by the funding program "MEDICUS", of the University of Patras. The authors would like to thank the Laboratory of Instrumental Analysis of the University of Patras for UHPLC-MS analysis.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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