*3.11. Characterization of Recyclable PBN@SiO<sup>2</sup>*

After arsenic elimination, the recycled PBN@SiO<sup>2</sup> was investigated with XRD, SEM, and FTIR to understand the effect of the recycling process on PBN@SiO<sup>2</sup> morphology, size, and crystallinity. An SEM image of the recycled PBN@SiO<sup>2</sup> is shown in Figure 12. More spherical-shaped than cube-shaped particles were observed; the aggregation of PBN with no precise shape was also observed. XRD analysis demonstrated a shifting inward of the peak position (θ) as compared with the unused PBN@SiO2. The presence of anticipated elements was identified via EDX analysis. In addition, characteristic CN stretching in PBN was noted; this feature was noted at a considerably lower wavenumber (2054 cm−<sup>1</sup> ), which is attributed to particle aggregation [39]. The PBN characteristics before and after the recycling process as obtained from XRD, SEM, and FTIR analysis are listed in Table 4.

and crystallinity. An SEM image of the recycled PBN@SiO2 is shown in Figure 12. More spherical-shaped than cube-shaped particles were observed; the aggregation of PBN with no precise shape was also observed. XRD analysis demonstrated a shifting inward of the peak position (θ) as compared with the unused PBN@SiO2. The presence of anticipated elements was identified via EDX analysis. In addition, characteristic CN stretching in PBN was noted; this feature was noted at a considerably lower wavenumber (2054 cm−1), which is attributed to particle aggregation [39]. The PBN characteristics before and after the recycling process as obtained from XRD, SEM, and FTIR analysis are listed in Table 4.

**Figure 12.** Analysis of recycled PBN@SiO2 following acid treatment. (**A**) An alteration in nanoparticle morphology as identified through SEM imaging, (**B**) A decrease in particle size (26 nm) as calculated from the displayed histogram, (**C**) Minor shift in peak position with similar planes as identified through XRD analysis, (**D**) Spectrum with the entire anticipated element as detected by EDX, (**E**) Shift in CN stretching peak observed using FTIR. **Figure 12.** Analysis of recycled PBN@SiO<sup>2</sup> following acid treatment. (**A**) An alteration in nanoparticle morphology as identified through SEM imaging, (**B**) A decrease in particle size (26 nm) as calculated from the displayed histogram, (**C**) Minor shift in peak position with similar planes as identified through XRD analysis, (**D**) Spectrum with the entire anticipated element as detected by EDX, (**E**) Shift in CN stretching peak observed using FTIR.

**Table 4.** Table with HRSEM, XRD and FTIR data displaying the variations between unused and recycled PBN@SiO2. **Table 4.** Table with HRSEM, XRD and FTIR data displaying the variations between unused and recycled PBN@SiO<sup>2</sup> .


### FTIR CN Str. 2096 cm−1 2054 cm−<sup>1</sup> **4. Conclusions**

**4. Conclusions**  PBN are a light-sensitive material that is processed through functional alkoxysilaneand cyclohexanone-mediated conversion of a single precursor, potassium hexacyanoferrate. The synthetic incorporation of PBN within mesoporous silica (PBN@SiO2) was also studied; the morphology of these particles was characterized using TEM, SEM, XRD, and XPS. The as-made PBN were studied as a fluorescent quencher. The quenching ability of the materials is found to be a function of arsenic (III) concentration; this result suggested a novel application of PBN for fluorescence sensing of arsenic. In addition, XPS studies confirmed that arsenic is adsorbed on PBN@SiO2 as arsenite (As(III)) and arsenate (As (V)) irrespective of the initial oxidation state of the material; this result indicated a novel ap-PBN are a light-sensitive material that is processed through functional alkoxysilaneand cyclohexanone-mediated conversion of a single precursor, potassium hexacyanoferrate. The synthetic incorporation of PBN within mesoporous silica (PBN@SiO2) was also studied; the morphology of these particles was characterized using TEM, SEM, XRD, and XPS. The as-made PBN were studied as a fluorescent quencher. The quenching ability of the materials is found to be a function of arsenic(III) concentration; this result suggested a novel application of PBN for fluorescence sensing of arsenic. In addition, XPS studies confirmed that arsenic is adsorbed on PBN@SiO<sup>2</sup> as arsenite (As(III)) and arsenate (As(V)) irrespective of the initial oxidation state of the material; this result indicated a novel application of PBN for the removal of arsenic(III) from a given sample.

plication of PBN for the removal of arsenic (III) from a given sample. **Author Contributions:** Conceptualization, P.C.P., S.S. and R.J.N.; methodology, P.C.P., S.S. and and R.J.N.; software, P.C.P., S.S. and R.J.N.; validation, P.C.P., S.S. and R.J.N.; formal analysis, P.C.P., S.S. and R.J.N.; investigation, P.C.P., S.S. and R.J.N.; resources, P.C.P., S.S. and R.J.N.; data curation, P.C.P., S.S. and R.J.N.; writing—original draft preparation, P.C.P., S.S. and R.J.N.; writing—review and editing, P.C.P., S.S. and R.J.N.; visualization, P.C.P., S.S. and R.J.N.; supervision, P.C.P., S.S. and R.J.N.; project administration, P.C.P., S.S. and R.J.N.; funding acquisition, P.C.P., S.S. and R.J.N. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by [SERB, DST and DRDO] grant number [VJR/2017/000034 and LSRB-316 respectively].

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Indian Institute of Technology (BHU), and approved by the Institutional Review Board.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** Data supporting reported results can be found in the laboratory of Prof. Prem C Pandey of IIT(BHU). https://iitbhu.ac.in/dept/apc/people/faculty.

**Acknowledgments:** The authors acknowledge IIT (BHU), Varanasi for financial assistance. Thanks are given to SERB for the VAJRA Fellowship and DRDO for granting LSRB-316.

**Conflicts of Interest:** The authors declare that they have no known competing financial interests or personal relationships that influence the work reported in this paper.

### **References**

