CN105107463A - Preparation of phosphotungstic acid composite material and experimental method for testing adsorbing performance of phosphotungstic acid composite material to methylene blue - Google Patents

Abstract

The invention discloses preparation of a phosphotungstic acid composite material and an experimental method for testing the adsorbing performance of the phosphotungstic acid composite material to methylene blue. Dawson type H6P2W18O62 and a metal organic skeleton MOF-5 serve as raw materials. An adsorbent H6P2W18O62/MOF-5 composite material is prepared through solvothermal, and representation is performed through IR, XRD, SEM and other means. The adsorbing performance of the phosphotungstic acid composite material to the methylene blue (MB) in an aqueous solution is researched, and influences of initial pH, temperature and MB in different initial concentrations on the adsorbing capacity are discussed. Compared with the prior art, the MOF-5 is modified through the H6P2W18O62, the organic skeleton composite material H6P2W18O62/MOF-5 is synthesized, the modified material has a good adsorbing effect on the methylene blue (MB), application prospects are provided for the situation that MOFs materials are used for liquid phase adsorption, and certain research significance is achieved.

Description

The preparation of phosphotungstic acid composite and to methylene blue adsorption number performance test method

Technical field

The present invention relates to a kind of metal experimental technique, particularly relate to a kind of MOF-5 load Dawson type phosphotungstic acid composite preparation and to methylene blue adsorption number performance test method.

Background technology

Dyestuff is in weaving, coating, food technology and hair-dyeing agent ^[1-8]be widely used etc. in industry, in the daily production process of these industries, certainly lead to a large amount of waste water from dyestuff, the main component in the waste water that caused dyestuff to become.Dyestuff has become the primary pollution source of each large Main River Systems at present in China.In dye families, numerous dyestuff is poisonous is even carcinogenic to human body, directly threatens the mankind itself.And along with the variation of dopant composition, its intractability also increases gradually.Finding a kind of processing method of novel waste water from dyestuff, is the current problem needing solution badly.

Domestic and international researcher, for solving a dye wastewater treatment difficult problem, has done a large amount of explorations and innovation.Such as by chemical oxidation, calcining, biodegradation, is separated, absorption etc. ^[9,10,11]chemistry, biological and physical processing techniques is applied in waste water from dyestuff improvement.Wherein, absorption is considered to the most directly, most effective method, and it can not only adsorb in waste water the dyestuff that is difficult to degrade and can also reclaim dyestuff, realizes recycling economy.The principle of absorption is that adsorbent has large hole and specific area, the dyestuff in organic wastewater being induced to enter the duct of adsorbent or be deposited on its surface, then reaching the object of purifying liquid waste by isolating adsorbent.

Metallic organic framework (MOFs) is the porous material that a class has adjustable aperture and large specific area, is widely used in catalysis and adsorbing domain.The synthetic technology of current MOF-5 is studied the most ripe.MOF-5 i.e. [Zn ₄o (BDC) ₃], be by Zn ₄o is by phenyl ring (part terephthalic acid (TPA) (H ₂bDC) provide) bridging and the complex with microcellular structure formed, because its specific area is huge, pore volume is high, advantage that the design of aperture structure, constitute and function is adjustable etc., demonstrates wide application prospect in the storage of gas, adsorbing separation and catalysis.The preparation method of MOFs material mainly comprises hydro-thermal method, microwave method, ultrasonic method, liquid phase diffusion method etc.The most frequently used synthetic method of MOFs is solvent heat (hydro-thermal) method, namely adds metal coordination ion, part and suitable solvent first in a kettle., stirring at room temperature a period of time, is then transferred in freeze-day with constant temperature baking oven by reactor and react a period of time.After reaction terminates, be cooled to room temperature.Reacted solution centrifugal is separated, with solvent wash adsorbent several, can adsorbent be obtained by after the adsorbent vacuum drying of having washed.The absorption property of existing bibliographical information MOF-5 mainly concentrates on Gas Phase Adsorption aspect, such as CO ₂, CH ₄, N ₂o and N ₂ ^[12]etc. the research of aspect.Have no bibliographical information and cross the absorption of MOF-5 in liquid phase.

Summary of the invention

Object of the present invention be just to provide to solve the problem a kind of phosphotungstic acid composite preparation and to methylene blue adsorption number performance test method.

The present invention is achieved through the following technical solutions above-mentioned purpose:

The present invention is characterized in that, comprises following methods:

Experiment reagent: sodium tungstate [Na ₂wO ₄2H ₂o], SPA, concentrated hydrochloric acid, absolute ether, zinc nitrate hexahydrate [Zn (NO ₃) ₂6H ₂o], terephthalic acid (TPA) [H ₂bDC], DMF, methylene blue, redistilled water;

Metallic organic framework composite H ₆p ₂w ₁₈o ₆₂the preparation of/MOF-5:

(1) preparation of Dawson type phosphotungstic acid: by dense for 35mL H ₃pO ₄(mass fraction is 85%) is added drop-wise to and is dissolved with 50gNa ₂wO ₄2H ₂in the 60mL aqueous solution of O, be heated to 120 DEG C and keep backflow 8h.After it fully cools, add excessive hydrochloric acid carry out acidifying, then with isopyknic ether, the liquid after acidifying is extracted, obtain phosphotungstic acid ether mixtures, carry out drying after little fire heating makes ether wherein volatilize, can light yellow solid be obtained, be H ₆p ₂w ₁₈o ₆₂xH ₂o (P ₂w ₁₈);

(2) hydro-thermal method prepares metallic organic framework composite H ₆p ₂w ₁₈o ₆₂/ MOF-5: by the Zn (NO of 0.149g ₃) ₂6H ₂the H of O (0.5mmol) and 0.0166g ₂the H of BDC (0.1mmol) and 0.05g ₆p ₂w ₁₈o ₆₂be added in reactor, then add 15mLN, dinethylformamide (DMF), stirring at room temperature 30min, then transferred in freeze-day with constant temperature baking oven by reactor and react 21h, reaction temperature is 120 DEG C.After reaction terminates, be cooled to room temperature.Reacted solution centrifugal is isolated adsorbent, and wash adsorbent 5-6 time with DMF, by the adsorbent vacuum drying 12h washed, baking temperature is 80 DEG C, can obtain adsorbent H ₆p ₂w ₁₈o ₆₂/ MOF-5;

The preparation of methylene blue standard liquid:

100mg/L methylene blue dye solution is diluted to the thin liquid that mass concentration is 2mg/L, 4mg/L, 6mg/L, 8mg/L, 10mg/L respectively, at maximum absorption wavelength (664nm) place, measure the absorbance of MB solution, rendering quality concentration-absorbance standard curve, linear equation is: Y=0.2026X+0.0502, R ²=0.9967;

Metallic organic framework composite H ₆p ₂w ₁₈o ₆₂/ MOF-5 adsorbs methylene blue solution experiment:

A certain amount of metallic organic framework composite H is added in methylene blue solution ₆p ₂w ₁₈o ₆₂/ MOF-5 carries out adsorption experiment, inquires into the initial pH of MB, and concentration and temperature are on the impact of absorption.Adsorption liquid measures absorbance after high speed centrifugation, by MB calibration curve and its adsorbance of following formulae discovery.

$q_e=\frac{(c_o-c_e)v1000}{m373.9}$

In formula: c ₀and c _efor the mass concentration (mg/L) of MB initially and when balancing; V, m, q _ebe respectively liquor capacity (L), adsorbent mass (g) and equilibrium adsorption capacity (μm ol/g).

Beneficial effect of the present invention is:

The present invention be a kind of phosphotungstic acid composite preparation and to methylene blue adsorption number performance test method, compared with prior art, the present invention passes through H ₆p ₂w ₁₈o ₆₂modified synthesis organic framework composite material H is carried out to MOF-5 ₆p ₂w ₁₈o ₆₂/ MOF-5, modified material is better to methylene blue (MB) solution adsorption effect, provides application prospect, have certain Research Significance for MOFs material is used for liquid phase adsorption.

Accompanying drawing explanation

Fig. 1 is the canonical plotting of methylene blue of the present invention;

Fig. 2 is H of the present invention ₆p ₂w ₁₈o ₆₂, MOF-5, H ₆p ₂w ₁₈o ₆₂the infared spectrum of/MOF-5;

Fig. 3 is H of the present invention ₆p ₂w ₁₈o ₆₂, MOF-5, H ₆p ₂w ₁₈o ₆₂the XRD collection of illustrative plates of/MOF-5;

Fig. 4 is MOF-5, H of the present invention ₆p ₂w ₁₈o ₆₂the TG figure of/MOF-5;

Fig. 5 is MOF-5, H of the present invention ₆p ₂w ₁₈o ₆₂the N of/MOF-5 ₂-adsorption desorption curve and graph of pore diameter distribution;

Fig. 6 is H of the present invention ₆p ₂w ₁₈o ₆₂(a, b), MOF-5 (c) and H ₆p ₂w ₁₈o ₆₂the SEM figure of/MOF-5 (d);

Fig. 7 is that pH of the present invention affects schematic diagram to MB adsorbance;

Fig. 8 is that temperature of the present invention affects schematic diagram to MB adsorbance;

Fig. 9 is that MB initial mass concentration of the present invention affects schematic diagram to adsorbance;

Figure 10 is MOF-5 and H of the present invention ₆p ₂w ₁₈o ₆₂the adsorption effect contrast schematic diagram of/MOF-5;

Figure 11 is the Langmuir absorption isotherm schematic diagram of methylene blue of the present invention;

Figure 12 is the plan first order kinetics schematic diagram under methylene blue variable concentrations of the present invention;

Figure 13 is the plan second-order kinetics schematic diagram under methylene blue variable concentrations of the present invention.

Detailed description of the invention

Below in conjunction with accompanying drawing, the invention will be further described:

The present invention is characterized in that, comprises following methods:

Experiment reagent: sodium tungstate [Na ₂wO ₄2H ₂o], SPA, concentrated hydrochloric acid, absolute ether, zinc nitrate hexahydrate [Zn (NO ₃) ₂6H ₂o], terephthalic acid (TPA) [H ₂bDC], DMF, methylene blue, redistilled water;

Metallic organic framework composite H ₆p ₂w ₁₈o ₆₂the preparation of/MOF-5:

(1) preparation of Dawson type phosphotungstic acid: by dense for 35mL H ₃pO ₄(mass fraction is 85%) is added drop-wise to and is dissolved with 50gNa ₂wO ₄2H ₂in the 60mL aqueous solution of O, be heated to 120 DEG C and keep backflow 8h.After it fully cools, add excessive hydrochloric acid carry out acidifying, then with isopyknic ether, the liquid after acidifying is extracted, obtain phosphotungstic acid ether mixtures, carry out drying after little fire heating makes ether wherein volatilize, can light yellow solid be obtained, be H ₆p ₂w ₁₈o ₆₂xH ₂o (P ₂w ₁₈);

(2) hydro-thermal method prepares metallic organic framework composite H ₆p ₂w ₁₈o ₆₂/ MOF-5: by the Zn (NO of 0.149g ₃) ₂6H ₂the H of O (0.5mmol) and 0.0166g ₂the H of BDC (0.1mmol) and 0.05g ₆p ₂w ₁₈o ₆₂be added in reactor, then add 15mLN, dinethylformamide (DMF), stirring at room temperature 30min, then transferred in freeze-day with constant temperature baking oven by reactor and react 21h, reaction temperature is 120 DEG C.After reaction terminates, be cooled to room temperature.Reacted solution centrifugal is isolated adsorbent, and wash adsorbent 5-6 time with DMF, by the adsorbent vacuum drying 12h washed, baking temperature is 80 DEG C, can obtain adsorbent H ₆p ₂w ₁₈o ₆₂/ MOF-5;

The preparation of methylene blue standard liquid:

100mg/L methylene blue dye solution is diluted to the thin liquid that mass concentration is 2mg/L, 4mg/L, 6mg/L, 8mg/L, 10mg/L respectively, at maximum absorption wavelength (664nm) place, measure the absorbance of MB solution, rendering quality concentration-absorbance standard curve (as Fig. 1), linear equation is: Y=0.2026X+0.0502, R ²=0.9967;

The calibration curve of Fig. 1 methylene blue.

Metallic organic framework composite H ₆p ₂w ₁₈o ₆₂/ MOF-5 adsorbs methylene blue solution experiment:

A certain amount of metallic organic framework composite H is added in methylene blue solution ₆p ₂w ₁₈o ₆₂/ MOF-5 carries out adsorption experiment, inquires into the initial pH of MB, and concentration and temperature are on the impact of absorption.Adsorption liquid measures absorbance after high speed centrifugation, by MB calibration curve and its adsorbance of following formulae discovery.

$q_e=\frac{(c_o-c_e)v1000}{m373.9}$

In formula: c ₀and c _efor the mass concentration (mg/L) of MB initially and when balancing; V, m, q _ebe respectively liquor capacity (L), adsorbent mass (g) and equilibrium adsorption capacity (μm ol/g).

Result and discussion

Metallic organic framework composite H ₆p ₂w ₁₈o ₆₂the sign of/MOF-5

IR analyzes

Fig. 2 H ₆p ₂w ₁₈o ₆₂, MOF-5, H ₆p ₂w ₁₈o ₆₂the infared spectrum of/MOF-5.

As shown in Figure 2, the major absorbance peak of MOF-5 is 3428.6cm ^-1, 1657.9cm ^-1, 1601.8cm ^-1, 1389.0cm ^-1, 823.4cm ^-1, 750.0cm ^-1, and pure H ₆p ₂w ₁₈o ₆₂major absorbance peak all with document ^[12,14]report is consistent.H ₆p ₂w ₁₈o ₆₂the absworption peak of/MOF-5 is 1673.2,1601,1384.3,823.4,750.0cm ^-1, except the basic framework characteristic absorption peak remaining MOF-5, also comprise Dawson phosphotungstic acid 1093.3cm ^-1v _as(P-O _a), 968.8cm ^-1v _as(W=O _d), 917.4cm ^-1v (W-O _b-W) characteristic absorption peak, H after load is described ₆p ₂w ₁₈o ₆₂still keep Dawson structure, phosphotungstic acid is present in the rigid frame of MOF-5 with guest molecule.

XRD analysis

Fig. 3 H ₆p ₂w ₁₈o ₆₂, MOF-5, H ₆p ₂w ₁₈o ₆₂the XRD collection of illustrative plates of/MOF-5.

H as shown in Figure 3 ₆p ₂w ₁₈o ₆₂xRD diffraction maximum mainly concentrate on 2 θ=7 ~ 10 °, in 14 ~ 20 ° of these 2 intervals, the characteristic diffraction peak of prepared MOF-5 sample and document ^[15]unanimously, and add H ₆p ₂w ₁₈o ₆₂do not impact the structure of MOF-5, hint MOF-5 has good ordered structure.Simultaneously at H ₆p ₂w ₁₈o ₆₂h is not detected in/MOF-5 ₆p ₂w ₁₈o ₆₂diffraction maximum, H is described ₆p ₂w ₁₈o ₆₂be highly dispersed in the duct of MOF-5.

TG analyzes

Fig. 4 MOF-5, H ₆p ₂w ₁₈o ₆₂the TG figure of/MOF-5.

As shown in Figure 4 along with rising MOF-5 and H of temperature ₆p ₂w ₁₈o ₆₂/ MOF-5 is weightless gradually.Be the process losing guest molecule from room temperature to 160 DEG C, mainly comprise: physical absorption water and the crystallization water; 160 DEG C of stages being exactly skeleton later and caving in gradually, relative to H MOF-5 ₆p ₂w ₁₈o ₆₂the temperature that/MOF-5 needs at this one-phase is higher, and H is described ₆p ₂w ₁₈o ₆₂load is in MOF-5 skeleton or be dispersed in the duct of MOF-5.

BET analyzes

The adsorption/desorption isotherms of the pure skeleton MOF-5 of Fig. 5 and compound.

As shown in Figure 5, the adsorption/desorption isotherms of pure skeleton MOF-5 and compound all belongs to IV type, and the appearance of hysteresis loop is due to capillary condensation effect, shows that these two kinds of materials all belong to mesoporous material.Analyzed by BJH method, draw its pore size distribution figure (the interior illustration of Fig. 5), average pore size (as shown in table 1) is respectively 2.057nm and 3.451nm and proves that both are mesoporous material further.From table 1, both specific areas and pore volume are not all very large, and the specific area of compound diminishes, and shows that compound is fewer than the hole of pure MOF-5, in conjunction with both the comparison of absorption property, further illustrate the absorption of this compound to MB and control by chemisorbed.

Table 1MOF-5 and H ₆p ₂w ₁₈o ₆₂the structural parameters of/MOF-5

Sem analysis

Fig. 6 H ₆p ₂w ₁₈o ₆₂(a, b), MOF-5 (c) and H ₆p ₂w ₁₈o ₆₂the SEM figure of/MOF-5 (d).

As shown in Figure 6, H ₆p ₂w ₁₈o ₆₂for shaggy class spherical (6a), and there is loose structure (6b), show its easy doping vario-property.The cube that MOF-5 is, its particle diameter is about 20 μm (6c), H ₆p ₂w ₁₈o ₆₂after being carried on MOF-5, pattern changes, and compound presents chondritic (6d) not of uniform size, hint H ₆p ₂w ₁₈o ₆₂be dispersed in the duct of MOF-5.

3.2H ₆p ₂w ₁₈o ₆₂/ MOF-5 adsorbs the research of methylene blue

The pH of methylene blue solution is on the impact of adsorption effect

Get 20mg adsorbent, vibrate in 20mL20mg/L methylene blue solution, investigate the impact that this adsorbent under different pH adsorbs methylene blue solution.

Fig. 7 pH is on the impact of MB adsorbance.

As can be seen from Figure 7 solution ph significantly affects the adsorption capacity of compound to methylene blue.Along with the increase adsorbance of pH is in reduction, low ph value is conducive to the absorption of methylene blue, and high pH suppresses MB absorption.Suction-operated is by adsorbent (H ₆p ₂w ₁₈o ₆₂/ MOF-5) and adsorbate (MB) between electrostatic interaction realize ^[16,17], and the impact of pH be mainly manifested in can change adsorbate and adsorbent surface with electric charge, thus affect adsorption effect.Through testing the Zeta potential of adsorbent, under the condition that acidity is stronger, draw H ₆p ₂w ₁₈o ₆₂/ MOF-5 surface band negative electrical charge is larger, and methylene blue surface band positive charge, so low ph value is conducive to the absorption of methylene blue.

Temperature is on the impact of adsorption effect

Get 15mg adsorbent, in the 30mg/L of 20mL, in the MB solution of 35mg/L, 40mg/L, 45mg/L, 50mg/L, after pH is adjusted to 2, investigate the impact of temperature on absorption.

Fig. 8 temperature is on the impact of MB adsorbance.

As shown in Figure 8, H ₆p ₂w ₁₈o ₆₂/ MOF-5 is increased to 145.38 μm ol/gs along with temperature raises from 137.68 μm of ol/g to the adsorbance of MB, and this illustrates that the process of absorption methylene blue is the process of heat absorption.Temperature raises and is conducive to H ₆p ₂w ₁₈o ₆₂the increase of/MOF-5 adsorbance, may be at relatively high temperatures, methylene blue molecule comes to life, and facilitates H ₆p ₂w ₁₈o ₆₂/ MOF-5 is to the absorption of methylene blue; In another aspect certain limit, the rising of temperature is to H ₆p ₂w ₁₈o ₆₂/ MOF-5 plays the effect of certain reaming, thus adsorbance is increased.

Initial concentration is on the impact of adsorption effect

Claim 15mg adsorbent, be respectively 20mg/L in 20mL concentration, regulate pH=2 to vibrate in the methylene blue solution of 25mg/L, 30mg/L, 35mg/L, 40mg/L, 45mg/L, every 10min surveys a sample, investigate MB initial mass concentration to the impact of absorption.

Fig. 9 MB initial mass concentration is on the impact of adsorbance.

As shown in Figure 9, H ₆p ₂w ₁₈o ₆₂the adsorbance of/MOF-5 increases along with the increase of MB initial concentration.This is because methylene blue solution concentration increases, H can be made ₆p ₂w ₁₈o ₆₂the concentration difference of/MOF-5 surface and solution main body increases, and the motive force of adsorbing is increased, thus adsorbance increases.

3.2.4MOF-5 with H ₆p ₂w ₁₈o ₆₂the adsorption effect contrast of/MOF-5

Get 15mgMOF-5 and H respectively ₆p ₂w ₁₈o ₆₂/ MOF-5 is in the methylene blue solution of 30mg/L in 20mL concentration and regulate pH=2 to vibrate, and every 10min surveys a sample, investigates MOF-5 and H ₆p ₂w ₁₈o ₆₂/ MOF-5 is to methylene blue adsorption number Contrast on effect.

Figure 10 MOF-5 and H ₆p ₂w ₁₈o ₆₂the adsorption effect contrast of/MOF-5.

As shown in Figure 10 when the concentration of methylene blue solution is 30mg/L, pH=2 the monolayer adsorption amount of MOF-5 than H ₆p ₂w ₁₈o ₆₂the monolayer adsorption amount of/MOF-5 is much smaller, and H is passed through in this explanation ₆p ₂w ₁₈o ₆₂carrying out modification to MOF-5 can make MOF-5 material for liquid phase adsorption, and carrying out this subject study is significantly.

The determination of Tellurium determination

On the basis inquiring into temperature impact, we further study two kinds of isotherm adsorption models (Langmuir and Freundlich) of MB.Wherein Langmuir linear equation ^[18]equation is as follows:

$\frac{C_e}{q_e}=\frac{1}{q_m}{C}_e+\frac{1}{q_m{K}_L}$

Q _eand q _m(mg/g) H when being balance respectively ₆p ₂w ₁₈o ₆₂the adsorbance of/MOF-5 and maximum monolayer adsorption amount, the concentration of methylene blue when Ce (mg/L) is balance, K _l(L/mg) be the absorption constant of Langmuir.By Ce to Ce/q _emapping (Figure 11), linear relationship shows H ₆p ₂w ₁₈o ₆₂/ MOF-5 adsorbs methylene blue and meets Langmuir Adsorption Model, and the relevant parameter calculated is in table 2.

The Langmuir absorption isotherm of Figure 11 methylene blue.

The fundamental characteristics of Langmuir isothermal adsorption, can use R _lvalue represent ^[19]

$R_L=\frac{1}{1+{\mathrm{bC}}_o}$

K _l(L/mg) be the absorption constant of Langmuir equation at constant temperature, C ₀(mg/L) be the initial concentration of dyestuff.

R _ldescribe corresponding isothermal adsorption capacity:

R _l>1 is unfavorable for absorption

0<R _l<1 good adsorption

R _l=0 Irreversible Adsorption

R _l=1 linear adsorption

The H adopted herein ₆p ₂w ₁₈o ₆₂/ MOF-5 adsorbs methylene blue at the R of 20 DEG C, 30 DEG C, 40 DEG C _lvalue is respectively: 0.9998,0.9997 and 0.9994, thus proves H ₆p ₂w ₁₈o ₆₂the absorption of/MOF-5 to methylene blue is good adsorption.

Freundlich absorption is an empirical equation.Freundlich Tellurium determination is generally expressed as:

${\mathrm{lnq}}_e=\frac{1}{n}{\mathrm{lnC}}_e+{\mathrm{lnK}}_F$

Wherein K _f(mol/g (L/mol) ^1/n) adsorption capacity indicating adsorbent roughly, 1/n describes the size of adsorption strength.Relevant parameter has been calculated in table 2.

The adsorption isothermal curve parameter of table 2 methylene blue

The relevant parameter of Langmuir, Freundlich two kinds of isotherm adsorption models has been calculated in table 2.More meet Langmuir isotherm adsorption model by data this experimental data known in table, and have bibliographical information ^[20]langmuir isotherm adsorption model is utilized to explain adsorbent absorbing dye from dye solution.

The determination of adsorption dynamics adsorption kinetics

In order to probe into the controlling mechanism of this adsorption process, experimental data is carried out matching by two kinds of kinetic models.

Intend First order dynamic model

Langmuir equation is a simple dynamic absorption analysis equation, can represent with following formula ^[21]:

$\frac{{\mathrm{dq}}_t}{dt}=k_1(q_e-q_t)$

K _lh ₆p ₂w ₁₈o ₆₂/ MOF-5 adsorbing filament technique (min ^-1), q _eand q _tthe amount (mg/g) of balance and t time, institute time absorbing dye respectively.The q when establishing t=0 _t=0 and t=t, q _t=q _t, then above formula can be deformed into:

ln(q _e-q _t)＝lnq _e-k _It

Can by t to ln (q _e-q _t) map and obtain k _i, as figure:

Plan first order kinetics under Figure 12 methylene blue variable concentrations.

H under 20mg/L and 30mg/L as can be known from Fig. 12 ₆p ₂w ₁₈o ₆₂the linearly dependent coefficient of the absorption plan First order dynamic model of/MOF-5 is respectively: 0.8145 and 0.91, experiment gained adsorbance q _ethe adsorbance q calculated with first order kinetics formula _t(concrete numerical value is in table 3) is completely inconsistent, therefore H is described ₆p ₂w ₁₈o ₆₂the absorption of/MOF-5 to methylene blue does not meet plan First order dynamic model, and therefore adsorption process is not diffusion-controlled phenomenon ^[22].

Intend second-order kinetics model

Intending second-order kinetics model linear equation is:

$\frac{t}{q_t}=\frac{1}{k_2{q_e}^2}+\frac{1}{q_e}t$

K ₂also be H ₆p ₂w ₁₈o ₆₂/ MOF-5 adsorbing filament technique (min ^-1), q _eand q _tthe same

Plan second-order kinetics under Figure 13 methylene blue variable concentrations

The numerical value of the adsorbance and theory calculate adsorbance (table 3) of testing gained MB as can be known from Fig. 13 matches, and the linearly dependent coefficient (R of the plan second-order kinetics model of gained ²) be all greater than 0.99, describe H ₆p ₂w ₁₈o ₆₂second-order kinetics model is intended in the absorption of/MOF-5 to MB, is controlled by chemisorbed.

Table 3MB intends first order kinetics and intends second motive force mathematic(al) parameter under variable concentrations

Thermodynamic parameter

H is carried out at 293K, 303K and 313K temperature ₆p ₂w ₁₈o ₆₂/ MOF-5 adsorbs the experiment of methylene blue, research adsorption equilibrium costant (k _l), Gibbs free energy (Δ G °), enthalpy change (Δ H °) and Entropy Changes (Δ S °), they can use following formulae discovery:

$K_L=\frac{q_e}{C_e}$

ΔG°＝-RTlnK _L

Wherein, R is 8.3145Jmol ^-1k ^-1, T is temperature (K).

According to equation Δ H ° can by 1/T to lnk with Δ S ° difference _lslope and the intercept of mapping calculate.Associated hot mechanics parameter is in table 4.

Table 4H ₆p ₂w ₁₈o ₆₂/ MOF-5 adsorbs the thermodynamic parameter of MB

From the data of table 4, it is spontaneous that a Δ G ° <0 shows to adsorb; Δ H ° of >0 illustrates that the process of absorbing dye is the process of a heat absorption, thus further confirms this experimental result.

Different adsorbent Contrast on effect

The adsorption capacity of the different adsorbent of table 5 to MB compares

The maximum monolayer adsorption amount of different adsorbent to MB compares by table 5, Q from table 5 _ebe worth known, H ₆p ₂w ₁₈o ₆₂the monolayer adsorption of/MOF-5 to MB is better than other adsorbents.Therefore H ₆p ₂w ₁₈o ₆₂/ MOF-5 is a kind of good MB adsorbent, has potential using value.

Conclusion

(1) H ₆p ₂w ₁₈o ₆₂the maximum monolayer adsorption amount of/MOF-5 to methylene blue is 58.26mg/g, has actual industrial application value.Raised temperature and reduction pH are conducive to H ₆p ₂w ₁₈o ₆₂/ MOF-5 is to the absorption of methylene blue, and thermodynamic parameter also demonstrates this conclusion.

(2) H ₆p ₂w ₁₈o ₆₂the absorption of/MOF-5 to MB meets Langmuir isotherm adsorption model, and its adsorption process is by intending second-order kinetics models fitting.It is spontaneous that dynamic experiment data Δ G ° of <0 shows to adsorb; Δ H ° of >0 illustrates that the process of absorbing dye is the process of a heat absorption.

More than show and describe general principle of the present invention and principal character and advantage of the present invention.The technical staff of the industry should understand; the present invention is not by the restriction of above-mentioned example; what describe in above-mentioned example and description just illustrates principle of the present invention; without departing from the spirit and scope of the present invention; the present invention also has various changes and modifications, and these changes and improvements all fall in the claimed scope of the invention.Application claims protection domain is defined by appending claims and equivalent thereof.

Claims (1)

1. phosphotungstic acid composite preparation and to a methylene blue adsorption number performance test method, it is characterized in that, comprise following methods:

Experiment reagent: sodium tungstate [Na ₂wO ₄2H ₂o], SPA, concentrated hydrochloric acid, absolute ether, zinc nitrate hexahydrate [Zn (NO ₃) ₂6H ₂o], terephthalic acid (TPA) [H ₂bDC], DMF, methylene blue, redistilled water;

Metallic organic framework composite H ₆p ₂w ₁₈o ₆₂the preparation of/MOF-5:

(1) preparation of Dawson type phosphotungstic acid: by dense for 35mL H ₃pO ₄(mass fraction is 85%) is added drop-wise to and is dissolved with 50gNa ₂wO ₄2H ₂in the 60mL distilled water of O, be heated to 120 DEG C and keep backflow 8h, after it fully cools, add excessive hydrochloric acid carry out acidifying, then with isopyknic ether, acidifying solution is extracted, obtain phosphotungstic acid ether mixtures, carry out drying after little fire heating makes ether wherein volatilize, can light yellow solid be obtained, be H ₆p ₂w ₁₈o ₆₂xH ₂o (P ₂w ₁₈);

(2) hydro-thermal method prepares metallic organic framework composite H ₆p ₂w ₁₈o ₆₂/ MOF-5: by the Zn (NO of 0.149g ₃) ₂6H ₂the H of O (0.5mmol) and 0.0166g ₂the H of BDC (0.1mmol) and 0.05g ₆p ₂w ₁₈o ₆₂be added in reactor, then add 15mLN, dinethylformamide (DMF), stirring at room temperature 30min, then transferred in freeze-day with constant temperature baking oven by reactor and react 21h, reaction temperature is 120 DEG C, after reaction terminates, be cooled to room temperature, reacted solution centrifugal is isolated adsorbent, washs adsorbent 5-6 time, by the adsorbent vacuum drying 12h washed with DMF, baking temperature is 80 DEG C, can obtain adsorbent H ₆p ₂w ₁₈o ₆₂/ MOF-5;

The preparation of methylene blue standard liquid:

100mg/L methylene blue dye solution is diluted to the thin liquid that mass concentration is 2mg/L, 4mg/L, 6mg/L, 8mg/L, 10mg/L respectively, at maximum absorption wavelength (664nm) place, measure the absorbance of MB solution, rendering quality concentration-absorbance standard curve, linear equation is: Y=0.2026X+0.0502, R ²=0.9967;

Metallic organic framework composite H ₆p ₂w ₁₈o ₆₂/ MOF-5 adsorbs methylene blue solution experiment:

A certain amount of metallic organic framework composite H is added in methylene blue solution ₆p ₂w ₁₈o ₆₂/ MOF-5 carries out adsorption experiment, inquires into the initial pH of MB, and concentration and temperature are on the impact of absorption, and adsorption liquid measures absorbance after high speed centrifugation, by MB calibration curve and its adsorbance of following formulae discovery,

$q_e=\frac{(c_o-c_e)v1000}{m373.9}$

In formula: c ₀and c _efor the mass concentration (mg/L) of MB initially and when balancing; V, m, q _ebe respectively liquor capacity (L), adsorbent mass (g) and equilibrium adsorption capacity (μm ol/g).