Dual-functional pyrene implemented mesoporous silicon material used for the detection and adsorption of metal ions

Jing Huang,Honghui Cai,Qian Zhao,Yunpeng Zhou,Haibo Liu,Jing Wang

School of Chemistry and Chemical Engineering,Guangxi University,Nanning 530004,China

Keywords:Dual function Nanomaterials Mesoporous silica Metal ions Detection and adsorption

ABSTRACT A fluorescent active organic-inorganic hybrid material PyN-SBA-15 was synthesized by implementing pyrene derivatives into mesoporous SBA-15 silica.PyN-SBA-15 had detection and removal functionalities toward Al3+,Cu2+,and Hg2+.On the one hand,PyN-SBA-15 was used as a fluorescence sensor and displayed high sensitivity toward Al3+,Cu2+,and Hg2+ cations (limit of detection: 8.0 × 10-7,1.1 × 10-7,and 2.9 × 10-6 mol.L-1,respectively) among various analytes with ‘‘turn-off” response.On the other hand,the adsorption studies for these toxic analytes (Cu2+,Hg2+,and Al3+) showed that the ion removal capacity could reach up to 45,581,and 85 mg.g-1,respectively.Moreover,the Langmuir isotherm models were better fitted with the adsorption data,indicating that the adsorption was mono-layer adsorption.Kinetic analysis revealed that the adsorption process was well described by the pseudo-second-order kinetic model for Cu2+ and Hg2+ and pseudo-first-order kinetic model for Al3+.The prepared silica material could be reused in four recycles without significantly decreasing its adsorption capacity.Therefore,the PyN-SBA-15 material can serve as a promising candidate for the simultaneous rapid detection and efficient adsorption of metal ions.

1.Introduction

Clean water resources play an important role in the life activities of plants and animals.However,with the increase of human activities and rapid industrial development,metal ions in industrial wastewater will enter drinking water resources,causing water pollution and posing a threat to the health of living things[1-3].As the most abundant metal element in the Earth’s crust,aluminum(Al3+) is widely distributed in the environment and is closely related to life activities[4].However,excessive Al3+in the environment will harm the normal growth of plants and the health of human beings [5,6].Cu2+is one of the trace elements necessary for various metabolic functions of living organisms.However,excessive amounts of Cu2+can cause a range of diseases,such as cardiovascular disease and atherosclerosis [7].Owing to the adverse effects of Cu2+,the World Health Organization (WHO) set the maximum acceptable concentration of Cu2+in drinking water to 2.0 mg.L-1[8].Heavy metal ions,such as mercury (Hg2+),are one of the most harmful pollutants and tend to accumulate in the body,causing severe damage to mental and psychological health and even death in humans [9].The US Environmental Protection Agency (EPA) has established a standard of 2×10-9for the permissible level of inorganic Hg2+ions in drinking water[10].Therefore,the real-time detection and effective removal of excessive metal ions from industrial wastewater before discharging are important issues related to health and environmental safety [11].

Considerable efforts are accordingly being devoted to exploiting new technologies for sensing and adsorbing these toxic ions.In the past few decades,a series of organic probes and materials has been used for the selective and sensitive detection of metal ions[12-16].However,the use of these probes is limited due to their complex synthesis,poor water solubility,and need for organic solvents.On the other hand,many types of nanomaterials have been developed as adsorbents for the removal of metal ions,such as covalent organic frameworks (COFs) [17],metal-organic frameworks(MOFs) [18],mesoporous silica materials [19],porous organic polymers (POPs) [20],and nanofibers [21].However,most of the reported methods can only be used for the single detection or removal of metal ions,which limits their practical applications.To achieve the purpose of simultaneous detection and removal,some dual-functional materials,such as MOFs [22],cationic organic network [23],and magnetic nanoparticles [24],have also been exploited in recent years.

Recently,organic-inorganic hybrid materials have attracted extensive attention because of their tunable properties due to the combination of organic molecules and inorganic materials [25].Among various hybrid materials,mesoporous silica (e.g.,SBA-15[26])exhibits excellent features such as high porosity,large specific surface area,orderly pore channels,and good stability.In addition,the abundance of hydroxyl groups on the surface of SBA-15 facilitates functionalization [27].Through covalent bond connection,various fluorescent molecules could be grafted into porous SBA-15 material.Thus,functional SBA-15 shows excellent fluorescence detection performance while maintaining the ordered pore structure of mesoporous materials[28,29].Moreover,the fascinating physical properties of SBA-15 make it an outstanding candidate material as a solid carrier with adsorption performance [30-32].Therefore,SBA-15 is a potential mesoporous material that could be used for the simultaneous detection and adsorption of metal ions.Nevertheless,several studies have focused on the single detection or removal of metal ions.Hence,it is of great significance to develop the dual-functional advantages of SBA-15 for the simultaneous detection and removal of metal ions.

Considering the dual-functional possibilities of SBA-15 mesoporous material,we investigated the functionalized mesoporous silicon material for the rapid detection and efficient adsorption of metal ions.Herein,we conveniently constructed pyrene-derived ligand on the channel surface of SBA-15 mesoporous silica to obtain the hybrid material PyN-SBA-15,and studied its detection and adsorption capacity toward noxious metal ions.The research showed that PyN-SBA-15 exhibited extreme sensitivity and low detection limit for metal ions(Cu2+,Hg2+and Al3+).The fluorescent ensemble of PyN-SBA-15,PyH-SBA-15,and PyU-SBA-15 was constructed to distinguish the metal ions of Cu2+,Hg2+,Al3+,and Co2+.Furthermore,PyN-SBA-15 showed high efficiency and recoverability in the removal of metal ions from an aqueous solution.

2.Experimental

2.1.Materials and instruments

SBA-15 was purchased from Nanjing XFNANO Materials Tech Co.,Ltd.(China) and applied directly.1-Pyrenecarboxaldehyde,formylhydrazine and 3-(aminopropyl) triethoxysilane (APTES)were purchased from Sigma-Aldrich(Shanghai,China)without further purification.Metal ions solutions are prepared from their chlorides.Analyze pure levels of solvents,i.e.,ethanol (EtOH),toluene and chloroform (CHCl3) were purchased from commercial suppliers.

2.2.Instruments

The small angle X-ray powder diffraction (SXRD) pattern was obtained on a Smartlab9K diffractometer (Rigaku,Japan) with Cu Kα radiation.Transmission electron microscopy(TEM)images carried out using JEM-2100F microscope (JEOL,Japan).The thermogravimetric analysis (TGA) was measured using a STA449-F5 TAQ600 instrument (Netzsch,Germany) at a 10 °C.min-1heating rate.Micrometrics ASAP 2460 instrument (Micrometrics,USA)was used to measure the nitrogen adsorption-desorption isotherms.The Fourier transform infrared (FT-IR) were recorded on 660-IR(ATR)FT-IR spectrophotometer(Varian,USA).Fluorescence spectra were examined by 960 MC spectroscopy (Shanghai Lengguang Technology Co.,Ltd.,China),with an excitation wavelength of 368 nm.Nuclear magnetic resonance (1H NMR) spectra was taken on a 600 MHz Bruker spectrometer with TMS as an internal standard.Mass spectra were tested on the Avance III HD500 instrument (Bruker,Germany).To determine metal ion concentrations,inductively coupled plasma optical emission spectrometer (ICPOES) analyses were performed on the Thermo instrument(ICAP7000,Thermo Scientific,USA).

2.3.Synthesis and characterization of PyN-SBA-15

Synthesisof PYF.0.35 mmol(0.0805g)of 1-pyrenecarboxaldehyde and excess formylhydrazine(0.70 mmol,0.42 g)were dissolved in 50 ml of ethanol,stirring for 30 h at room temperature.After atmospheric filtration,the crude product was cleaned with ethanol several times to obtain pure (pyren-1-ylmethylene)formohydra zide (abbreviated as PYF) (Fig.1).Mass spectra:m/z[M+H]+calculated: 273.0,found: 273.1 (Fig.S1 in Supplementary Material).1H NMR (500 MHz,DMSO-d6) δ 9.93 (s,1H),9.29 (d,J=9.4 Hz,1H),8.85 (d,J=8.1 Hz,1H),8.45 (ddd,J=11.3,7.8,3.3 Hz,5H),8.36 (s,1H),8.31 (d,J=8.9 Hz,1H),8.18 (d,J=7.7 Hz,1H),5.76(s,1H) (Fig.S2).

Fig.1.Schematic illustration of the procedure for the preparation of PYF and PyN-SBA-15.

Synthesis of PyN-SBA-15.The synthesis of APTES-SBA-15 was based on the method described in the literature previously reported by our group (Fig.1) [33].Whereafter,0.4 g APTES-SBA-15 was weighed and stirred in 30 ml toluene for 10 min,then 1 mmol (0.272 g) of PYF was added to the mixture,and refluxed for 24 h at 110 °C.The product was cleaned with CHCl3and centrifuged to remove excess PYF.PyN-SBA-15 was obtained after drying at 80°C.Compared with TGA curve of the original SBA-15[34],the amount of organic part (functional group,C21H18N3,MW: 312 g.mol-1) of PyN-SBA-15 is 22.83% (mass).Therefore the moles of organic groups per gram of SBA-15 is calculated to 22.83%/312=0.73 mmol.Namely,the amount of functional group in SBA-15 is 0.73 mmol.g-1(Fig.S3).

2.4.Fluorescence studies

For fluorescence studies,0.5 ml of PyN-SBA-15 suspension(0.5 g.L-1,suspended in aqueous medium)was mixed with various analytes in aqueous buffer solution individually and sonicated for 20 min.The obtained suspension mixtures were allowed to stand at room temperature for 12 h before fluorescence measurement.This process was repeated before each fluorescence measurement.The fluorescence measurements were carried out by using an excitation wavelength at 368 nm.

2.5.Adsorption of metal ions

Adsorption experiments were carried out in an aqueous system at room temperature to determine adsorption parameters,such as adsorption isotherms and kinetic models.In a typical experiment,5 mg of PyN-SBA-15 was added to 10 ml aqueous solutions containing different concentrations of metal ions (i.e.,10-100 mg·L-1Cu2+,Al3+and 20-600 mg.L-1Hg2+).Then the mixtures were stirred for 12 h at room temperature to ensure that the adsorption reaches equilibrium,centrifuged and filtered with 0.45 μm membrane.The final concentration of various metal ions was measured by ICPOES.The equilibrium adsorption capacity is calculated using the equation.

whereqe(mg.g-1)is the equilibrium adsorption capacity,C0andCe(mg.L-1) are the initial and final concentration of metal ions in an aqueous solution,Vis the volume of the solution (L),andmis the mass of the material (g).

The adsorption isotherms were analyzed with the Langmuir and Freundlich isotherm model.The Langmuir isotherm model applies to monolayer adsorption,whereas the Freundlich isotherm model describes heterogeneous surfaces.whereqeandqmax(mg.g-1)are the equilibrium adsorption capacity and the maximum adsorption capacity,respectively.Ce(mg.L-1) is the equilibrium metal concentrations.KL(L.mg-1) is the Langmuir adsorption constant.KFis the Freundlich constant related to the adsorption capacity of the adsorbent andnis a heterogeneity parameter of the adsorbent surface.Langmuir equation separation factor(RL)is defined asRL=1∕(1+KLC0).Where,KLis the Langmuir adsorption isothermal constant,C0is the initial concentration of metal ions,whenRL＞1,the adsorption system is considered inappropriate,0 ＜RL＜1,the adsorption system is appropriate,whenRL=1,the adsorption system is linear,RL=0,the adsorption system is irreversible.

Kinetic studies for Al3+,Cu2+and Hg2+were conducted to determine the kinetic model.The process was as follows: 5 mg of sorbent PyN-SBA-15 were dispersed in 10 ml Al3+,Cu2+or Hg2+solution with the same initial concentration (100 mg.L-1).Each of the mixtures was continuously stirred for 15,30,60,90,120,180 min at room temperature.The analyte concentrations in the filtrate were analyzed by ICP-OES for kinetic models.Two kinetic models,i.e.,the pseudo-first-order and pseudo-second-order which can be expressed as Eqs.(4) and (5),respectively.

whereqtandqe(mg.g-1)are the amounts of adsorbed at timetand at equilibrium,respectively.K1(min-1) andK2(g.mg-1.min-1) are the rate constants for the pseudo-first-order constant and pseudosecond-order model,respectively.

2.6.The calculation of limit of detection(LOD)and quenching constant(KSV)

The calculation of theoretical detection limit according to the equation LOD=3σ/k,where σ is standard deviation of blank solutions of PyN-SBA-15 measured by ten times,andkis the slope of fluorescence intensityversus[Mn+] plot.A linear quenching equationF0/F=KSV[m]+1 and exponential quenching equationF0/F=A.eKSV[m]+Bwere used to fit the linear and nonlinear Stern-Volmer curve and calculate the quenching constant (KSV)of PyN-SBA-15 toward Mn+.In this equation,F0is the initial fluorescence intensity of the PyN-SBA-15,Fis the fluorescence intensity of PyN-SBA-15 after addition of Mn+,[m] is the concentration of Mn+.

3.Results and Discussion

The chemical structures of three organic-inorganic hybrid materials,namely,PyN-SBA-15,PyU-SBA-15,and PyH-SBA-15,and their corresponding solid-state images are shown in Fig.2.As for the organic part of these three materials,the fluorophores were pyrene.The solid-state fluorescent colors varied by changing the metal coordination groups.Specifically,PyN-SBA-15,PyU-SBA-15,and PyH-SBA-15 showed yellow,yellow-green,and blue color,respectively,under 365 nm UV light irradiation.The synthetic scheme and procedures of PyN-SBA-15 are given in Fig.1 and Section 2.3,respectively.The detailed synthetic procedures and characterizations of PyU-SBA-15 and PyH-SBA-15 had been reported in our previous research [33,35].

Fig.2.Chemical structures (a) and solid-state photographs of PyN-SBA-15,PyU-SBA-15,and PyH-SBA-15 under day light (b) and 365 nm UV light irradiation (c).

3.1.Characterization of PyN-SBA-15

Fig.3(a)shows the SXRD pattern of PyN-SBA-15.Three typically distinct reflections are(1 0 0),(1 1 0),and(2 0 0)planes,revealing a hexagonal mesoscopic organization which was consistent with the original SBA-15[34,36].The TEM image of PyN-SBA-15 clearly showed the well-ordered silica walls with pores (Fig.S4),demonstrating that the functionalized mesoporous silicon material still preserved the structures of original SBA-15 [34].The N2adsorption-desorption isotherms of SBA-15 and PyN-SBA-15 displayed a typical type IV isotherm(Fig.3(b)),with clear H1 hysteresis loop at higher relative pressure,which is the prototypical property of mesoporous materials [37].Moreover,compared with SBA-15,the surface area,pore size,and pore volume of PyN-SBA-15 decreased (Table S1).

Fig.3.(a) SXRD pattern and (b) N2 adsorption-desorption isotherms of PyN-SBA-15.

Fig.4 displays the FT-IR spectra of SBA-15,PYF,and PyN-SBA-15.For SBA-15 and PyN-SBA-15,the peak around 3437 cm-1could be attributed to the typical stretching vibrations of Si-OH[34].The peak at 805 cm-1was caused by the asymmetric stretching vibration of Si-OH.Two apparent bands at 467 and 1081 cm-1were associated with the stretching and bending vibrations of Si—O—Si,and the peak at 1630 cm-1was caused by the physical water absorption of the material.And the peak at 3037 cm-1was attributed to the unsaturated alkane peaks (=C-H) on pyrene [34].Compared with SBA-15,in the spectra of PyN-SBA-15,the additional peaks at 692,1564,and 1631 cm-1were attributed to the N-H stretching and bending vibrations,the band at 1474 cm-1was due to the C-N vibration of alkyl amine,and the peaks at 2922 and 2851 cm-1were attributed to the saturated alkane peaks(C-H) on APTES.The presence of all characteristic peaks in the spectra of PyN-SBA-15 indicated that PYF was successfully grafted and cleaned.These results indicated that the pyrene fluorophore and nitrogenous and carbonaceous functional groups had been successfully grafted onto the channel of SBA-15 and that the mesoporous structure was well preserved.

Fig.4.FT-IR spectra of SBA-15,PYF,and PyN-SBA-15.

3.2..Optimization of application conditions

The normalized emission spectra of PyN-SBA-15 showed monomer emission of pyrene at 383 and 399 nm and excimer emission of pyrene at 474 nm.To better present the spectral information,the excitation wavelength of 368 nm was used for the following studies (Fig.5).

Fig.5.Normalized emission and excitation spectra of PyN-SBA-15 (0.05 g.L-1) in aqueous solution (20 mmol.L-1 HEPES buffer,pH=6.0).

To ensure the stability of PyN-SBA-15 during the fluorescence detection,the detection conditions,such as time and pH values,were studied.pH had an obvious effect on the fluorescence of PyN-SBA-15,and the fluorescence intensity at 383 and 474 nm was relatively stable in the pH range of 6.0-11.0 (Fig.S5).The emission peak at 474 nm increased as a function of time,which could be attributed to the aggregation of pyrene fluorophore within the limited mesopores.However,the monomer emission of pyrene at 383 and 399 nm was almost unaffected by time.Thus,the time of 12 h and pH of 6.0 were used for the subsequent experiments,unless otherwise stated.

3.3.Sensing studies

As shown in Fig.6,the fluorescent response of PyN-SBA-15 toward metal ions was studied in aqueous solution (HEPES buffer,pH=6.0).Among 12 kinds of investigated metal ions,the fluorescence of PyN-SBA-15 displayed minimal or almost no changes in the presence of Na+,K+,Mg2+,Ca2+and Ba2+;the monomer emission peaks of pyrene at 383 and 399 nm quenched to varying degrees in the presence of Ni2+,Cd2+,Zn2+and Co2+;whereas the two monomer peaks dramatically quenched in the presence of Al3+,Cu2+,and Hg2+.Moreover,the fluorescence quenching of PyN-SBA-15 by Al3+,Cu2+,and Hg2+was investigated in the presence of competitive metal ions (Figs.S6 and S7).The fluorescent changes (F/F0) of PyN-SBA-15 by Al3+,Cu2+,and Hg2+changed in the presence of 3.0 equiv.other ions,someF/F0even changed to be more than 1.3 (Fig.S6).While the fluorescence quenching of PyN-SBA-15 by Al3+,Cu2+,and Hg2+was not affected in the presence of 2.0 equiv.competitive metal ions (Fig.S7),indicating that this material has a good anti-interference performance in response to Al3+,Cu2+,and Hg2+metal ions,when the concentration of the interfering substances was below 2.0 equiv.[38-40].Then,the titration experiments of PyN-SBA-15 toward different concentrations of Al3+,Cu2+,and Hg2+were carried out to determine the limit of detection (LOD) and Stern-Volmer quenching constants (Ksv) of the three kinds of metal ions.

Fig.6.Fluorescence spectra of PyN-SBA-15 (0.05 g.L-1) in the presence of various metal ions(1.0×10-4 mol.L-1)in the aqueous solution(20 mmol.L-1 HEPES buffer,pH=6.0).

As shown in Fig.7(a),the fluorescence intensity of PyN-SBA-15 at 383 nm gradually decreased with increasing Al3+concentration.When the Al3+concentration ranged from 0 to 4.0 × 10-5mol.L-1,the fluorescence intensity at 383 nmversusthe concentration of Al3+showed a good linear relationship (Fig.7(b)).The same phenomena were also observed for the titration of Hg2+and Cu2+(Figs.S8 and S9).The LODs of three metal ions were calculated to be 8.0 × 10-7mol.L-1(Al3+),1.1 × 10-7mol.L-1(Cu2+),and 2.9 × 10-6mol.L-1(Hg2+).In addition,the Stern-Volmer (SV) plot for Al3+was nonlinear (Fig.7(c)),whereas linear Stern-Volmer plots were observed for Cu2+and Hg2+(Fig.S10).A positive deviation of the SV plot from linearity indicated that the quenching mechanism for Al3+was either static or a combination of static and dynamic.A linear fitting for Cu2+and Hg2+suggests a static mechanism.TheKsvvalues were calculated,and the results are shown in Table 1.The nonlinearKsvfor Al3+was found to be 2.4×104L.mol-1,and the linearKsvfor Cu2+and Hg2+were calculated to be 1.2 × 105and 7.1 × 103L.mol-1,respectively.

Table 1 Detection linear range,LOD,and Ksv of PyN-SBA-15 toward metal ions

Fig.7.(a) Fluorescence spectra of PyN-SBA-15 (0.05 g.L-1) in the presence of different concentrations of Al3+ in aqueous solution (HEPES buffer,20 mmol.L-1,pH=6.0)(λex=368 nm).(b) Fluorescence intensity of PyN-SBA-15 (0.05 g.L-1) at 383 nm versus the concentration Al3+.(c) Nonlinear Stern-Volmer plot for Al3+.

As shown in Fig.8,the organic functionalized mesoporous silicon exhibited different response ability to metal ions by retaining the pyrene fluorophore in the organic function,but varying the metal ion coordination groups.As stated above,PyN-SBA-15 could respond to three kinds of metal ions (Al3+,Cu2+and Hg2+).However,it is difficult to distinguish the three metal ions through fluorescent response of PyN-SBA-15.Similar to PyN-SBA-15,PyHSBA-15 was sensitive to Cu2+,Hg2+,and Co2+,but did not have the ability to distinguish between them [34].Conversely,PyUSBA-15 exhibited excellent selectivity toward Hg2+by introducing carbonyl group as an additional metal coordination site [37].

Fig.8.Relative emission intensity of PyN-SBA-15,PyH-SBA-15,and PyU-SBA-15 to various metal ions (1.0 × 10-4 mol.L-1).

To recognize various metal ions selectively and sensitively,a fluorescent sensor ensemble composed of PyN-SBA-15,PyH-SBA-15,and PyU-SBA-15 was constructed (Fig.9).In the first channel,PyU-SBA-15 could selectively recognize Hg2+through the ‘‘turnoff” fluorescent signals;in the second channel,PyN-SBA-15 could differentiate the metal ions into two groups.On the one hand,‘‘turn-off” fluorescent signals were observed toward Cu2+and Al3+.On the other hand,no fluorescent signal was observed toward Co2+.In the third channel,PyH-SBA-15 distinguished Cu2+and Al3+by monitoring the fluorescent signals of ‘‘turn-off” and ‘‘no response,” respectively.

Fig.9.Discrimination of four metal ions by PyU-SBA-15,PyN-SBA-15,and PyH-SBA-15.

3.4.Adsorption studies

3.4.1.Adsorptionisotherm

Materials with high detection and adsorption performance of hazardous species are of great importance.Considering that functionalized mesoporous materials are rich in nitrogen-based ligands and can effectively bind with metal ions,PyN-SBA-15 may be used for metal ion removal.Thus,a series of adsorption experiments including the adsorption isotherm and the adsorption kinetic studies was carried out at room temperature to evaluate the adsorption capacity of metal ions.

To evaluate the maximum adsorption capacity for metal ions,adsorption isotherm studies were carried out,and the equilibrium adsorption capacity was calculated according to the equationq=(C0-C)V∕m.As shown in Fig.10,the adsorption capacity of Al3+,Cu2+,and Hg2+increased with increasing equilibrium concentration,and the maximum adsorption capacities measured in the experiments were 85,45,and 581 mg.g-1,respectively.Langmuir and Freundlich models were used to analyze the adsorption isotherms of the three metal ions,and the isotherm parameters are compared in Table 2.The correlation coefficient obtained by the Langmuir model was higher than that of the Freundlich model,which indicated that the adsorption of the three metal ions on PyN-SBA-15 was monolayer adsorption.The maximum fitting adsorption capacities of Al3+,Cu2+,and Hg2+were 257,87,and 1245 mg.g-1,respectively.The adsorptionRLvalues of the three metal ions were all between 0 and 1,concluding that the adsorbent has good adsorption performance for Al3+,Cu2+,and Hg2+.

Table 2 Langmuir and Freundlich adsorption parameters for metal ions

Fig.10.Adsorption isotherms of PyN-SBA-15 material toward (a) Al3+,(b) Cu2+,and (c) Hg2+.

3.4.2.Adsorptionkinetics

Then,the influence of contact time on the adsorption of PyNSBA-15 toward metal ions was studied to investigate the kinetic behavior.The initial concentration of metal ions was 100 mg.L-1,and the adsorbent dosage was 5 mg.As shown in Fig.S11,the concentration of metal ions decreased significantly in the first 15 min due to the abundant adsorption sites on PyN-SBA-15 at the beginning of adsorption,which could rapidly combine with metal ions.The adsorption reached equilibrium about 3,3 and 2 h for Al3+,Cu2+and Hg2+,and PyN-SBA-15 achieved the best adsorption toward Hg2+with a removal rate of up to 82%.

The quasi-first-order and quasi-second-order kinetic models were used to further analyze the adsorption kinetics.The fitting results were shown in Fig.11,and the kinetic constantKand linear correlation coefficientR2are shown in Table 3.The pseudo-firstorder correlation coefficient (R2=0.9920) of PyN-SBA-15 for Al3+was greater than the pseudo-second-order correlation coefficient(R2=0.9887),indicating that the adsorption process was mainly physical adsorption,whereas the adsorption process of Cu2+and Hg2+was more in line with the second-order kinetic model,indicating that the adsorption process was mainly chemical adsorption.Adsorption is controlled by the chemical interaction of electron sharing or transfer between adsorbent and adsorbate.The kinetic constants in the table indicate that the adsorption rate of Hg2+is the fastest.

Table 3 Kinetic parameters for Al3+,Cu2+,and Hg2+ adsorption onto PyN-SBA-15

Fig.11.Adsorption kinetic curves of (a) Al3+,(b) Cu2+,and (c) Hg2+ by pseudo-first-order model and pseudo-second-order model.

3.5.Recyclability study

The reproducibility of materials is one of the important factors that evaluate the material economy.Therefore,recycling experiments were carried out to evaluate the material reusability.Hg2+was selected to conduct four cycles of adsorption-desorption experiments due to its good adsorption performance on PyNSBA-15.During the desorption process,PyN-SBA-15 was recycled by using 0.1 mol.L-1EDTA and deionized water as desorption medium.The results showed a slight decrease in the adsorption capacity and removal rate after four cycles (Fig.12).Good recyclability suggests that PyN-SBA-15 has the potential to be an economical and stable adsorbent for adsorbing metal ions from water.In addition,the detection and adsorption of metal ions by PyN-SBA-15 was compared with other nanomaterials.As can be seen from Table S2,compared to most of the reported materials,PyN-SBA-15 exhibits good performance: (1) PyN-SBA-15 can achieve dual detection and adsorption abilities toward three metal ions;(2)comparable detection limits;(3) higher Hg2+adsorption capacity.

4.Conclusions

In summary,an organic functionalized mesoporous silica material,namely,PyN-SBA-15,with fluorescence activity was prepared by combining pyrene ligand PYF with mesoporous silica SBA-15.PyN-SBA-15 realized dual functions of detection and removal of Al3+,Cu2+,and Hg2+.PyN-SBA-15 responded to Al3+,Cu2+,and Hg2+ions with ‘‘turn-off” fluorescence signals and could achieve the quantitative detection of Al3+,Cu2+,and Hg2+with low LODs of 8.0 × 10-7,1.1 × 10-7,and 2.9 × 10-6mol.L-1,respectively.The adsorption of Al3+,Cu2+,and Hg2+on PyN-SBA-15 accorded with the Langmuir adsorption model and had higher saturated adsorption capacity(qmax=257,87,and 1245 mg.g-1,respectively)and faster adsorption kinetics.In addition,PyN-SBA-15 exhibited prominent adsorption and recycling performance after four adsorption-desorption cycles,making it an excellent adsorbent for the removal of metal ions.

Data Availability

No data was used for the research described in the article.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (21966006).

Supplementary Material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cjche.2023.01.014.