3.1.2. PBN Confined in Mesoporous Silica (PBN@SiO2)

We also attempted to insert PBN into mesoporous silica through the synergistic action of EETMSi and cyclohexanone; the product is represented as PBN@SiO2. Mesoporous silica with a particle size of 50 micrometers and a pore diameter of 6 nm was used for the synthetic insertion of PBN; these materials have use in column chromatography. SEM micrographs in Figure 2A–C show the topographical features of PBN@SiO<sup>2</sup> and the narrow size distribution of the PBN in the SiO<sup>2</sup> matrix. Figure 2D shows the EDX data for

low.

*2.4. Fluorometric Method* 

**3. Results and Discussion** 

PBN@SiO2, which shows a silicon content of 31.9% elemental weight; the inset of Figure 2A shows photographic images of mesoporous SiO<sup>2</sup> (I) and PBN@SiO<sup>2</sup> (II). The XRD spectra of as-made PBN@SiO<sup>2</sup> and mesoporous SiO<sup>2</sup> are shown in Figure 2E(a–b). The results for as-made PBN@SiO<sup>2</sup> and mesoporous SiO<sup>2</sup> demonstrate a broad peak, which is assigned to the 101 plane of amorphous SiO<sup>2</sup> (Figure 2E(a)); additional peaks for as-made PBN@SiO<sup>2</sup> are assigned to 220, 220 and 400 lattice planes of crystalline PBN. After exposure to the EETMSi-mediated PBN-laden formulation, an alteration in the SiO<sup>2</sup> pore size was detected via BET analysis (Table 1). quently, 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane (EETMSi) was used to make PBN in the absence of cyclohexanone [9]. Although the process enabled efficient conversion of single precursor, K3[Fe(CN)6, into Prussian blue nanoparticles, the duration was substantially longer. Accordingly, we attempted to use cyclohexanone along with EETMSi to obtain PBN from a single precursor pathway. Indeed, the process enabled the rapid formation of PBN, as shown in Figure 1; additional details on this process are provided be-

*Nanomaterials* **2021**, *11*, x FOR PEER REVIEW 4 of 20

*3.1. Organotrialkoxysilane-Mediated Synthesis of PBN Analogs* 

hemispherical analyzer with a delayline detector (SPECS Surface Nano Analysis GmbH, Berlin, Germany). The C-1s peak (284.5 eV) was used as an internal reference to calibrate the absolute binding energy. The quantitative detection of elements was performed through ICP techniques. Fluorescence analysis was performed using a 7100 spectrophotometer (Hitachi, Tokyo, Japan). Arsenic speciation was performed using high-performance liquid chromatography (HPLC) with a Shim-packed GIST C18 chromatography column encompassing a hydrophobic (non-polar) stationary phase (column length = 75 mm, inner diameter = 7.6 mm) for the determination of all species. Ammonium phosphate solution was used as an eluent for the entire HPLC experiment. The HPLC mobile phases of ammonium phosphate solution with pH 6.9 were prepared by mixing monobasic

(NH4H2PO4) and dibasic ((NH4)2HPO4) salt solutions with an appropriate ratio.

A fluorometric method was used for the determination of As(III) species. Fluorescein

(Flo) was used as a probe molecule (λex = 480 nm, λem = 510 nm) for the estimation of As(III) species. The fluorescence experiment was performed under neutral pH (6.8) conditions using Milli-Q water. Different concentrations of As(III) standard solution (10 ppm to 320 ppm) were prepared by adding appropriate amounts of sodium arsenite to Milli-Q water. The result was obtained using the effective concentration of Flo, PBN, and As(III).

K3[Fe(CN)6, into Prussian blue nanoparticles under ambient conditions [20]. Subse-

**Figure 1.** TEM images of PBN at different magnifications (**A**,**B**). Bar histogram displaying the particle size distribution curve of the nanoparticles (inset of Figure 1A). SAED pattern of as-synthesized particles (**C**), EDX profile with all the anticipated elements (**D**), XRD of EETMSi-functionalized PBN (**E**).


**Table 1.** Parameters calculated from BET nitrogen gas adsorption isotherm.

3.1.3. PBN-Doped Mesoporous Silica Nanoparticles (PBN@MSNP)

We also undertook the synthetic incorporation of PBN within mesoporous silica nanoparticles. Silica nanoparticles (MSNP) with an average particle size of 200 nm and a pore size of 6 nm were used for this purpose. The porous nanocomposite was obtained primarily in two steps: (a) surface functionalization of the matrix by EETMSi, followed by (b) the uniform distribution of metal precursor throughout the network and subsequent reduction to form nanoscale particles. The in situ growth of PBN was pH controlled. The soluble Fe3+ species easily adhered to the pore channels in the presence of capping agent EETMSi. The HRTEM micrograph of bare MSNPs (Figure 3a(A)) shows a porous skeleton of spherical morphology. Figure 3a(B) shows PBN inside the mesoporous silica nanoparticles (encircled in red) [26]. The selected area electron diffraction (SAED) pattern of the corresponding hybrid nanoparticle assembly (PBN@MSNP) is shown in Figure 3a(C).

The zeta potential value was obtained from dynamic light scattering (DLS) data to understand the solution stability of particles. As shown in Figure 3a(D), the value of zeta potential is nearly −23 mV (i.e., towards the negative side); hence, the PBNPs are also negatively charged. *Nanomaterials* **2021**, *11*, x FOR PEER REVIEW 6 of 20

**Figure 2.** (**A**,**B**) HRSEM images of PBN@SiO2 at two different magnifications. Inset of (**A**) shows photographic images of mesoporous silica (I) and PBN-inserted mesoporous silica (II). (**C**) The particle size distribution of PBN within mesoporous silica. (**D**) The EDX spectrum of PBN-inserted mesoporous silica. (**E**) XRD spectra of SiO2 (**a**) and PBN@SiO2 (**b**). **Figure 2.** (**A**,**B**) HRSEM images of PBN@SiO<sup>2</sup> at two different magnifications. Inset of (**A**) shows photographic images of mesoporous silica (I) and PBN-inserted mesoporous silica (II). (**C**) The particle size distribution of PBN within mesoporous silica. (**D**) The EDX spectrum of PBN-inserted mesoporous silica. (**E**) XRD spectra of SiO<sup>2</sup> (**a**) and PBN@SiO<sup>2</sup> (**b**).

3.1.3. PBN-Doped Mesoporous Silica Nanoparticles (PBN@MSNP) We also undertook the synthetic incorporation of PBN within mesoporous silica nanoparticles. Silica nanoparticles (MSNP) with an average particle size of 200 nm and a pore size of 6 nm were used for this purpose. The porous nanocomposite was obtained primarily in two steps: (a) surface functionalization of the matrix by EETMSi, followed by (b) the uniform distribution of metal precursor throughout the network and subsequent reduction to form nanoscale particles. The in situ growth of PBN was pH controlled. The The EDX spectrum of PBN@MSNPs is shown in Figure 3a(E). The EDX mapping of the organotrialkoxysilane-functionalized PBN@MSNPs with the elemental composition of (B) carbon, (C) nitrogen, (D) oxygen (E) iron, and (F) silicon is shown in Figure 3b. The crystallographic data for as-prepared PBN@MSNPs and blank MSNPs are shown in Figure 3a(F). The peaks indexed at 2θ values of 17.6◦ (200), 24.3◦ (220), and 37.8◦ (400) indicated the successful insertion of crystalline PBN within the SiO<sup>2</sup> matrix; per JCPDS # 73-0687, 17.4◦ (200), 24.7◦ (220), 35.3◦ (400), 39.6◦ (420), and 43.7◦ (422), 50.0◦ (440), 53.9◦ (600), 57.2◦ (620), 66.1◦ (640), 68.9◦ (642), and 77.2◦ (820) can be indexed as the PB cubic space group Fm3m.

### soluble Fe3+ species easily adhered to the pore channels in the presence of capping agent *3.2. FTIR Analysis of PBN@SiO<sup>2</sup>*

charged.

EETMSi. The HRTEM micrograph of bare MSNPs (Figure 3a (A)) shows a porous skeleton of spherical morphology. Figure 3a (B) shows PBN inside the mesoporous silica nanoparticles (encircled in red) [26]. The selected area electron diffraction (SAED) pattern of the corresponding hybrid nanoparticle assembly (PBN@MSNP) is shown in Figure 3a (C). The zeta potential value was obtained from dynamic light scattering (DLS) data to understand the solution stability of particles. As shown in Figure 3a (D), the value of zeta potential is The peak at 2086 cm−<sup>1</sup> in the FTIR spectrum (Figure 4A of PBN may be attributed to the CN stretching mode of the Fe(II)-C-N-(III)Fe moiety in PBN. The broad bands at 3402 cm−<sup>1</sup> and 1642 cm−<sup>1</sup> in the spectrum correspond to OH-stretching and H2O bending mode of the interstitial water molecule, respectively, within the PBN lattice. The strong band near 2885–2990 cm−<sup>1</sup> corresponds to the C-H stretching vibration of sp<sup>2</sup> -hybridized carbon in cyclohexanone.

nearly –23 mV (i.e., towards the negative side); hence, the PBNPs are also negatively

(**b**)

**Figure 3.** (**a**) (**A**) HRTEM image of organotrialkoxysilane-functionalized Prussian blue nanoparticles (PBN@MSN), (**B**) micrograph showing the magnified view of bulk-confined PBN (encircled in red) in mesoporous silica, (**C**) SAED pattern of the corresponding hybrid nanoparticle assembly (PBN@MSN), (**D**) stability profile of PBN@MSN in terms of zeta potential measurement, and (**E**) EDX spectrum of PBN@MSNP. (**F**) XRD profile for MSNPs (i) and as-synthesized PBN@MSNPs (ii). (**b**) (**A**) Mapping analysis of organotrialkoxysilane-functionalized Prussian blue nanoparticles with elemental composition (**B**) carbon, (**C**) nitrogen, (**D**) oxygen (**E**) iron, and (**F**) silicon. **Figure 3.** (**a**) (**A**) HRTEM image of organotrialkoxysilane-functionalized Prussian blue nanoparticles (PBN@MSN), (**B**) micrograph showing the magnified view of bulk-confined PBN (encircled in red) in mesoporous silica, (**C**) SAED pattern of the corresponding hybrid nanoparticle assembly (PBN@MSN), (**D**) stability profile of PBN@MSN in terms of zeta potential measurement, and (**E**) EDX spectrum of PBN@MSNP. (**F**) XRD profile for MSNPs (i) and as-synthesized PBN@MSNPs (ii). (**b**) (**A**) Mapping analysis of organotrialkoxysilane-functionalized Prussian blue nanoparticles with elemental composition (**B**) carbon, (**C**) nitrogen, (**D**) oxygen (**E**) iron, and (**F**) silicon.

The EDX spectrum of PBN@MSNPs is shown in Figure 3a (E). The EDX mapping of the organotrialkoxysilane-functionalized PBN@MSNPs with the elemental composition of

**Figure 4.** (**A**) FTIR spectrum of as-synthesized PBN; (**B**) FTIR spectra of (black line) SiO2 and (red line) as-synthesized PBN@SiO2. **Figure 4.** (**A**) FTIR spectrum of as-synthesized PBN; (**B**) FTIR spectra of (black line) SiO<sup>2</sup> and (red line) as-synthesized PBN@SiO<sup>2</sup> .

The broad bands centered at 3548 cm**−**1 and at 1632 cm**−**1 are assigned to the stretching and bending vibrations of silanol groups (Si–OH), respectively, in the silica beads [27]. The bands at 1093 cm**−**1 and 801 cm**−**1 in the spectrum are associated with the anti-symmetric and symmetric stretching modes (Si–O–Si) of SiO4 units. The prominent peak at 2096 cm**−**1 (Figure 4 (B) is attributed to the stretching mode of Fe(II)-CN-(III)-Fe moiety in PBN [28] and indicates the successful formation of nanoparticles over SiO2. The broad bands centered at 3548 cm−<sup>1</sup> and at 1632 cm−<sup>1</sup> are assigned to the stretching and bending vibrations of silanol groups (Si–OH), respectively, in the silica beads [27]. The bands at 1093 cm−<sup>1</sup> and 801 cm−<sup>1</sup> in the spectrum are associated with the anti-symmetric and symmetric stretching modes (Si–O–Si) of SiO<sup>4</sup> units. The prominent peak at 2096 cm−<sup>1</sup> (Figure 4B is attributed to the stretching mode of Fe(II)-CN-(III)-Fe moiety in PBN [28] and indicates the successful formation of nanoparticles over SiO2.

(B) carbon, (C) nitrogen, (D) oxygen (E) iron, and (F) silicon is shown in Figure 3b. The crystallographic data for as-prepared PBN@MSNPs and blank MSNPs are shown in Figure 3a (F). The peaks indexed at 2θ values of 17.6° (200), 24.3° (220), and 37.8° (400) indicated the successful insertion of crystalline PBN within the SiO2 matrix; per JCPDS # 73-0687, 17.4° (200), 24.7° (220), 35.3° (400), 39.6° (420), and 43.7° (422), 50.0° (440), 53.9° (600), 57.2° (620), 66.1° (640), 68.9° (642), and 77.2° (820) can be indexed as the PB cubic space group Fm3m.

The peak at 2086 cm**−**1 in the FTIR spectrum (Figure 4 (A) of PBN may be attributed to the CN stretching mode of the Fe(II)-C-N-(III)Fe moiety in PBN. The broad bands at 3402 cm**−**1 and 1642 cm**−**1 in the spectrum correspond to OH-stretching and H2O bending mode of the interstitial water molecule, respectively, within the PBN lattice. The strong band near 2885–2990 cm**−**1 corresponds to the C-H stretching vibration of sp2-hybridized

### *3.3. Fluorometric Study*

*3.2. FTIR Analysis of PBN@SiO2* 

carbon in cyclohexanone.

### *3.3. Fluorometric Study*  3.3.1. Effect of the Addition of As(III) on the Fluorescent Intensity of Fluorescein

3.3.1. Effect of the Addition of As(III) on the Fluorescent Intensity of Fluorescein Since PBN have already been established as light quenching material, the PBN-mediated fluorescence quenching of fluorescein was evaluated. The impact of As(III) on fluorophore activity was studied via adding a different concentration of As(III) solution to a fixed Flo concentration. Subsequently, 0.01 mL of As(III) (10–320 ppm) and 10 μL of Flo solution (0.2 mM) were transferred into 2 mL of Milli-Q water and allowed to stand for 2 min at room temperature prior to fluorescence analysis. The fluorescence intensity of Flo was found to be enhanced as the function of As(III) (Figure 5A,B). At a lower As(III) concentration, a less pronounced enhancement phenomenon was observed. This result revealed that the extent of the interaction between Flo molecule and As(III) occurred to a Since PBN have already been established as light quenching material, the PBNmediated fluorescence quenching of fluorescein was evaluated. The impact of As(III) on fluorophore activity was studied via adding a different concentration of As(III) solution to a fixed Flo concentration. Subsequently, 0.01 mL of As(III) (10–320 ppm) and 10 µL of Flo solution (0.2 mM) were transferred into 2 mL of Milli-Q water and allowed to stand for 2 min at room temperature prior to fluorescence analysis. The fluorescence intensity of Flo was found to be enhanced as the function of As(III) (Figure 5A,B). At a lower As(III) concentration, a less pronounced enhancement phenomenon was observed. This result revealed that the extent of the interaction between Flo molecule and As(III) occurred to a higher extent at a higher As(III) concentration (up to 1.5 fold). The emission intensity was found to enhanced three-fold when the concentration of As(III) was elevated from 0.05 ppm to 2 ppm (effective concentration). *Nanomaterials* **2021**, *11*, x FOR PEER REVIEW 9 of 20

higher extent at a higher As(III) concentration (up to 1.5 fold). The emission intensity was

mM); the mixture was allowed to stand at room temperature for 2 min. The results revealed that PBN quenched the fluorescence property of Flo as shown in Figure 5C. Furthermore, the effect of PBN concentration over the emission intensity of Flo was investigated. Mixtures containing various concentrations of PBN with Flo were used to understand the interaction of nanoparticles with the fluorophore. The mixtures (i) PBN (0.06 mM) with Flo (0.2 mM) and (ii) PBN (0.3 mM) with Flo (0.2 mM) were evaluated. It was shown that EETMSi functionalized PBN acted as a quencher for Flo since the intensity of the fluorophore was found to diminish in the presence of PBN (Figure 5C). On increasing the concentration of PBN from 0.06 mM to 0.3 mM, only a small reduction in the emission

To understand the active role of PBN over As(III) interaction, we performed two experiments. In the first experiment, different concentrations of As(III) varying from 0.05 ppm to 1.6 ppm (effective concentration) were added to the fixed content of Flo (0.3 mM); the Flo-As(III) system was then exposed to a constant amount of PBN (0.3 mM) (as shown in Figure 6). In the second experiment, PBN (0.3 mM) were initially added to the Flo solution (0.2 mM); a variable concentration of As(III) between 0.05 ppm and 1.6 ppm (effective concentration) was then added to the PBN-Flo system (Figure 7). The substantial fluorescence quenching of the Flo-As(III) system in the presence of PBN was calculated using the relation F0/F, where F0 and F denote the fluorescent intensity of the Flo-As(III) system in the absence and in the presence of PBN, respectively (Figure 8A). Similarly, the substantial fluorescence quenching of the Flo system in the presence of PBN was calculated using the relation F0/F, where F0 denotes the fluorescence intensity of the Flo system in the absence of PBN and As(III), and F denotes the fluorescence intensity of Flo in the presence of PBN

**Figure 5.** Fluorescence emission spectra of Flo (blank) in the presence of different As(III) concentrations from 0.05 ppm to 1.6 ppm (**A**). Plot of fluorescence intensity of Flo (0.2 mM) after exposure to a variable concentration (0.05–1.6 ppm) of As(III) (**B**). Effect of PBN addition (0.06 mM, 0.3 mM) over Flo (0.2 mM) fluorescence (**C**). **Figure 5.** Fluorescence emission spectra of Flo (blank) in the presence of different As(III) concentrations from 0.05 ppm to 1.6 ppm (**A**). Plot of fluorescence intensity of Flo (0.2 mM) after exposure to a variable concentration (0.05–1.6 ppm) of As(III) (**B**). Effect of PBN addition (0.06 mM, 0.3 mM) over Flo (0.2 mM) fluorescence (**C**).

3.3.2. Interaction of Fluorophore with PBN

intensity was observed (Figure 5C).

and As(III) (Figure 8B).

3.3.3. Effect of As(III)/PBN System over Flo Intensity

(0.3 mM).

### 3.3.2. Interaction of Fluorophore with PBN

PBN were employed to observe the effect of the nano-sized particles over Flo. A constant amount of PBN nanosol (0.3 mM) was added to a known concentration of Flo (0.2 mM); the mixture was allowed to stand at room temperature for 2 min. The results revealed that PBN quenched the fluorescence property of Flo as shown in Figure 5C. Furthermore, the effect of PBN concentration over the emission intensity of Flo was investigated. Mixtures containing various concentrations of PBN with Flo were used to understand the interaction of nanoparticles with the fluorophore. The mixtures (i) PBN (0.06 mM) with Flo (0.2 mM) and (ii) PBN (0.3 mM) with Flo (0.2 mM) were evaluated. It was shown that EETMSi functionalized PBN acted as a quencher for Flo since the intensity of the fluorophore was found to diminish in the presence of PBN (Figure 5C). On increasing the concentration of PBN from 0.06 mM to 0.3 mM, only a small reduction in the emission intensity was observed (Figure 5C).

### 3.3.3. Effect of As(III)/PBN System over Flo Intensity

To understand the active role of PBN over As(III) interaction, we performed two experiments. In the first experiment, different concentrations of As(III) varying from 0.05 ppm to 1.6 ppm (effective concentration) were added to the fixed content of Flo (0.3 mM); the Flo-As(III) system was then exposed to a constant amount of PBN (0.3 mM) (as shown in Figure 6). In the second experiment, PBN (0.3 mM) were initially added to the Flo solution (0.2 mM); a variable concentration of As(III) between 0.05 ppm and 1.6 ppm (effective concentration) was then added to the PBN-Flo system (Figure 7). The substantial fluorescence quenching of the Flo-As(III) system in the presence of PBN was calculated using the relation F0/F, where F<sup>0</sup> and F denote the fluorescent intensity of the Flo-As(III) system in the absence and in the presence of PBN, respectively (Figure 8A). Similarly, the substantial fluorescence quenching of the Flo system in the presence of PBN was calculated using the relation F0/F, where F<sup>0</sup> denotes the fluorescence intensity of the Flo system in the absence of PBN and As(III), and F denotes the fluorescence intensity of Flo in the presence of PBN and As(III) (Figure 8B). *Nanomaterials* **2021**, *11*, x FOR PEER REVIEW 10 of 20

**Figure 6.** Study of the impact of PBN addition (10<sup>−</sup><sup>l</sup> ) over the emission intensity of Flo-As(III) system by varying the As(III) solution (0.05–1.6 ppm) and keeping a constant concentration of Flo (0.2 mM) and PBN (0.3 mM). **Figure 6.** Study of the impact of PBN addition (10−<sup>l</sup> ) over the emission intensity of Flo-As(III) system by varying the As(III) solution (0.05–1.6 ppm) and keeping a constant concentration of Flo (0.2 mM) and PBN (0.3 mM).

**Figure 7.** Study of the influence of As(III) addition over the emission spectra of the quenched Flo-PBN system by adding different concentrations of As(III) solution (0.05–1.6 ppm) and keeping a constant concentration of Flo (0.2 mM) and PBN

solution (0.05–1.6 ppm) and keeping a constant concentration of Flo (0.2 mM) and PBN (0.3 mM).

) over the emission intensity of Flo-As(III) system by varying the As(III)

**Figure 7.** Study of the influence of As(III) addition over the emission spectra of the quenched Flo-PBN system by adding different concentrations of As(III) solution (0.05–1.6 ppm) and keeping a constant concentration of Flo (0.2 mM) and PBN (0.3 mM). **Figure 7.** Study of the influence of As(III) addition over the emission spectra of the quenched Flo-PBN system by adding different concentrations of As(III) solution (0.05–1.6 ppm) and keeping a constant concentration of Flo (0.2 mM) and PBN (0.3 mM). *Nanomaterials* **2021**, *11*, x FOR PEER REVIEW 11 of 20

**Figure 8.** Bar diagram displaying fluorescence quenching (FQ) with respect to the variable concentration (effective concentration) of As(III) for the PBN@Flo-As(III) system (**A**) and the As(III)@PBN-Flo system (**B**). Plots of fluorescence intensity of the Flo-PBN system with respect to a variable content of As (III), showing concentration-dependent fluorescence quenching in both circumstances (**A-I**,**B-I**), with error bars representing the standard deviation. Emission spectra displaying the effect of adding 2 ppm of As(III) to the emission intensity of Flo (**C**). The required amount of PBN for complete quenching by adding various amounts of PBN to the Flo-As(III) system (**C-I**) and Flo. **Figure 8.** Bar diagram displaying fluorescence quenching (FQ) with respect to the variable concentration (effective concentration) of As(III) for the PBN@Flo-As(III) system (**A**) and the As(III)@PBN-Flo system (**B**). Plots of fluorescence intensity of the Flo-PBN system with respect to a variable content of As(III), showing concentration-dependent fluorescence quenching in both circumstances (**A-I**,**B-I**), with error bars representing the standard deviation. Emission spectra displaying the effect of adding 2 ppm of As(III) to the emission intensity of Flo (**C**). The required amount of PBN for complete quenching by adding various amounts of PBN to the Flo-As(III) system (**C-I**) and Flo.

*3.4. As(III) Decontamination from Aqueous Solution Using PBN@SiO2* 

tained both PBN.

It was observed that As(III) interacted predominately with the available quantity of

The heterogeneous PBN@SiO2 system was studied in order to understand the dynamic interaction occurring between As(III) and PBN. Accordingly, inexpensive and nonreactive silica beads were used for the modulation of active PBN in the formulation of the heterogeneous matrix. Heterogeneous methods are considered to play an influential role in catalysis due to their straightforward separation and large-scale applicability. For As(III) decontamination, the as-synthesized PBN@SiO2 (0.05 g) was successfully packed in a column of 10 mm diameter. The standard As(III) solution (10 ppm) was prepared via adding an appropriate amount of sodium arsenite salt in Milli-Q water; 10 mL of the solution was passed through the PBN@SiO2 enclosed column. The fluorescence analysis of separated supernatant (PBN@SiO2 processed) was performed using Flo (0.2 mM) under

intensity after interacting with Flo (Figure 8C-I). The subsequent addition of PBN achieved maximum quenching after interacting with available As(III), as displayed in Figure 8C-I. This result indicates that 0.54 mM PBN was sufficient to obtain complete interaction with 2 ppm arsenite. A similar concentration of 2 ppm of As(III) was added to the Flo-PBN system, which contained both PBN and Flo. The results (Figure 8A-I and Figure 8B-I) showed a decrease in fluorescent intensity of Flo-As(III) and Flo as a function of PBN; PBN altered the fluorescence influencing properties of As(III). It is surmised that Prussian blue interacted with As(III) more efficiently than the Flo-As system throughout the fluorescence process. A separate experiment was performed to discover the PBN loading for complete removal of As(III) from a concentration of 2 ppm (effective concentration). For this study, primary emission spectra of Flo-As(III) were recorded while adding As(III) aqueous solution (2 ppm) to the blank solution containing Flo (0.2 Mm) only (Figure 8C). A similar concentration of 2 ppm of As(III) was added to the Flo-PBN system, which con-

It was observed that As(III) interacted predominately with the available quantity of the PBN moiety; the residual available As(III) was associated with the rise in emission intensity after interacting with Flo (Figure 8C-I). The subsequent addition of PBN achieved maximum quenching after interacting with available As(III), as displayed in Figure 8C-I. This result indicates that 0.54 mM PBN was sufficient to obtain complete interaction with 2 ppm arsenite. A similar concentration of 2 ppm of As(III) was added to the Flo-PBN system, which contained both PBN and Flo. The results (Figure 8A-I and Figure 8B-I) showed a decrease in fluorescent intensity of Flo-As(III) and Flo as a function of PBN; PBN altered the fluorescence influencing properties of As(III). It is surmised that Prussian blue interacted with As(III) more efficiently than the Flo-As system throughout the fluorescence process. A separate experiment was performed to discover the PBN loading for complete removal of As(III) from a concentration of 2 ppm (effective concentration). For this study, primary emission spectra of Flo-As(III) were recorded while adding As(III) aqueous solution (2 ppm) to the blank solution containing Flo (0.2 Mm) only (Figure 8C). A similar concentration of 2 ppm of As(III) was added to the Flo-PBN system, which contained both PBN.
