Surface and Colloid Chemistry PDF

SURFACE and COLLOID CHEMISTRY Prof. Dr. Orhan OZDEMIR December 2024  Adsorption ▪ An increase in the concentration of surfactant molecules, ions, etc. on the surfaces of minerals or on the interfaces such as air- water is called «ADSORPTION»....

SURFACE and COLLOID CHEMISTRY Prof. Dr. Orhan OZDEMIR December 2024  Adsorption ▪ An increase in the concentration of surfactant molecules, ions, etc. on the surfaces of minerals or on the interfaces such as air- water is called «ADSORPTION». ▪ The substance adsorbed on the Adsorbates surface is called an adsorbent, and the substance attached to the surface is called an adsorbate. ▪ Adsorbent: The material that does the adsorption process ADSORBENT (activated carbon). SURFACE ▪ Adsorbate: The substance which is adsorbed on the adsorbent (metal ions in water).  Adsorption ▪ An accumulation of ions / molecules on the surface and interfaces. Gas adsorption on solid surfaces Mineral Surface Surfactant adsorption at mineral surface Surfactant adsorption at liquid / air interface  Adsorption of Solutes from Solutions Macropores (> 50 nm) Micropores (< 2 nm) Mesopores (2-50 nm) ▪ Solid substances (adsorbents) adsorb dissolved substances (solutes) from solutions.  Adsorption at Solid / Liquid Interface ▪ Adsorption of ions from solution at mineral / water interface depends on chemical composition of mineral surface, crystal sturucture, and charge distribution in the electrical double layer. ▪ If a chemical reaction between species in solution and ions constituing mineral surface occurs this is called chemical bonding and the type of uptake is called chemical adsorption. ▪ If adsorption occurs through adsorption of counter ions in electrical double layer it is called physical adsorption.  Differences between Physical and Chemical Adsorption PHYSICAL ADSORPTION: ▪The forces of attraction holding the adsorbate are Vander Waal’s forces. ▪Bonding between molecules and surface is by weak van der Waals forces. CHEMICAL ADSORPTION: ▪The forces of attraction holding the adsorbate are chemical bond forces. ▪Chemical bond is formed between molecules and surface.  Differences between Physical and Chemical Adsorption Physical Adsorption Chemical Adsorption Adsorbent and crystal lattice are Adsorbent and crystal lattice form a single two separate systems phase Adsorption heat is 3-4 kcal/mol Adsorption heat is 10-1000 kcal/mol Binding is very weak Binding is very strong Occurs at low temperature Occurs at high temperature No electron sharing Involve sharing of electrons between adsorbent and adsorbed molecules Reversible reaction Irreversible reaction More than one layer Only one layer Physical Adsorption Chemical Adsorption  Factors affecting adsorption from solution at the S/L interface ▪ Solute concentration ▪ Temperature ▪ Surface area of adsorbent ▪ pH of the solution ▪ Pressure ▪ Time  Applications of Adsorption ❑ Among the widely used industrial adsorbents, the most important of the adsorbents currently used for controlling environmental pollution are active carbon with high porosity. ❑ ACTIVATED CHARCOAL SILICA AND ALUMINA GELS  What is «Adsorption Isotherm»? ❑ The process of Adsorption is usually studied through graphs know as adsorption isotherm. ❑ It is the graph between the amounts of adsorbate (x) adsorbed on the surface of adsorbent (m) and concentration Concentrat at constant temperature. Concentration ❑ Different adsorption isotherms have been Freundlich, Langmuir and BET theory.  What is «Adsorption Isotherm»? ❑ In the process of adsorption, adsorbate gets adsorbed on adsorbent. From the graph, we can predict that after certain concentration, adsorption does not occur anymore. This can be explained by the fact that there are limited numbers of vacancies on the surface of the Concentration adsorbent. At high concentration a stage is Concentration reached when all the sites are occupied and further increase in concentration does not cause any difference in adsorption process.  Surfactants at the Solid-Liquid Interface Low Concentration - Surfactant Adsorption Moderate Concentration - Hemimicelle Formation High Concentration - Self-Assembled Surface Aggregates  Specific Interactions: Chain-Chain As surface concentration of ionic surfactant increases, if attractive hydrophobic interactions between alkyl chains can compensate for ionic head group repulsion, hemimicelles can form. At low coverages, patches can form on the surface. _ _ _ _ _ _ _ _ + + + ++ +  Quartz-Amine Adsorption Adsorption Density (mol/cm2) Region I Region II Bölge Region III III Region III Bölge RegionI I DAH Concentration (mol/L or M)  Adsorption Experiments ▪ Adsorption tests are conducted in containers (such as glass vials, bottles, etc.) with the adsorbents at certain adsorption conditions. ▪ In this case, first, a certain amount of adsorbent such as clay mineral is added into a glass vial filled with distilled and deionized water (The solid concentrations should be 0.1%). ▪ Next, the desired amount of chemicals at different concentrations is added to the suspension. ▪ Then, the glass vials are placed on an orbital shaker, and the suspension is mixed at 400 rpm for 4 h at room temperature. ▪ Then, the suspension is filtered by centrifugation for 10 min to obtain the solution which will be used to determine the remaining concentration of the adsorbate/solute. ▪ Then, the equilibrium concentrations of chemicals are determined using such as a visible spectrophotometer. ▪ And, finally, the adsorption density is calculated by the following formula:  Adsorption Experiments 𝐶𝑖 − 𝐶𝑓. 𝑉 Adsorption Density 𝛤= 𝑚. 𝑆 Γ: Adsorption density (mol/cm2 or mol/g) Ci: Initial concentration of solution (mol/L) Cf: Final concentration of solution (mol/L) V: Solution volüme (L) m: Adsorbent amount (g) S: Surface area of adsorbent (m2/g) (BET)  Preparation of clay / chemical suspension Ci: 1 ppm concentration V: 10 mL solution m: 0.01 g clay (S/L: 0.1%) S: 65 m2/g Mixing at 400 rpm in the orbital mixer for 240 min Transfer suspension to the vacuum pump filtration system A vacuum pump filtration system  Transfer suspension to the vacuum pump filtration system ▪ Now, the final concentration of the solution can be determined using a UV-visible spectrometer.  UV/Vis Chemical Analysis 𝐶𝑖 − 𝐶𝑓. 𝑉 𝛤= 𝑚. 𝑆 After UV analysis, the final concentration of the solution is determined as «Absorbance value».  UV/Vis Chemical Analysis Solution ▪ The basic logic of the spectrophotometer is based on the principle of transmitting light in certain spectrums from the prepared solutions and finding out how much of this light is absorbed by the solution. ▪ Therefore, spectrophotometric measurements in the UV – visible region are one of the most used methods in qualitative and quantitative analysis.  UV/Vis Chemical Analysis ▪ Lights between 190 and UV Region Visible Region 400 nm in wavelength are detected in the UV Peak value: 552 nm field. Adsorbance ▪ Lights between 400 and 700 nm wavelengths in the visible area can be seen with the eye. 190-400 nm -> UV Region 400-700 nm -> Visible Wavelength (nm) Region  UV/Vis Chemical Analysis 1.8 Chemical 1.6 Absorbance Concentration Value 1.4 (ppm) 1 0.027 1.2 Absorbance Value 5 0.082 10 0.155 25 0.395 1.0 50 0.781 y = 0.0153x + 0.0087 0.8 100 1.536 R² = 0.9999 0.6 0.4 0.2 0.0 0 20 40 60 80 100 120 Chemical Concentration (ppm)  Calculation adsorption 1.8 density for solutions after the 1.6 adsorption experiments ??? 10 mL=0.01 L Table. Results for adsorption 1.4 experiments 0.01 g Cf 1.2 Cf Adsorption Ci Absorbance Value Absorbance Density 0.1% solid concentration (0.01 g sepiolite in 10 mL chemical (ppm) (ppm) Value 1.0 (mg/g) solutions) 1 0.018 0.61 0.39 y = 0.0153x + 0.0087 10 0.149 0.8 R² = 0.9999 concentration (Cf) + 0.0087 Absorbance Value = 0.0153.Chemical 25 0.302 50 0.409 0.6 Cf = (Absorbance Value - 0.0087)/0.0153 100 0.565 250 1.255 0.4 Cf = (0.018- 0.0087)/0.0153 500 4.955 For 1 ppm 750 8.754 0.2 Cf = 0.61 ppm (mg/L) 1000 12.583 0.0 (mg/L-mg/L) 0 20 40 L 60 80 100 120 HTAB Concentration (ppm) 𝐶𝑖 − 𝐶𝑓. 𝑉 1 − 0.61. 0.01 𝛤 = 𝟎. 𝟑𝟗 𝒎𝒈/𝒈 𝛤= 𝛤= 𝑚. 𝑆 0.01 g  Measurement of Surface Area (BET) ▪ The specific surface area of sample is determined by BET (Brunauer, Emmett and Teller) which relates to the total surface area (reactive surface) as all porous structures adsorb the small gas molecules at a given pressure. ▪ The BET method is based on adsorption of gas on a surface. ▪ The amount of gas adsorbed allows to determine the surface area. ▪ It is a cheap, fast and reliable method. ▪ It is very well understood and applicable in many fields. (mg/L-mg/L) L 𝐶𝑖 − 𝐶𝑓. 𝑉 1 − 0.61. 0.01 𝛤 = 𝟎. 𝟎𝟎𝟔 𝒎𝒈/𝒎𝟐 𝛤= 𝛤= 𝑚. 𝑆 0.01. (65) g m2/g  Calculation of Adsorption Density Example 1: Adsorption experiments were carried out at 1.10-4 M HTAB concentration with sepiolite. The following are the experimental conditions: Ci: 1.10-4 mol/L V: 20 mL m: 100 mg (S/L: 0.5%) S: 65 m2/g After UV analysis the final concentration was determined using UV-visible spectrometer. Cf: 1.10-5 mol/L Calculate the adsorption density.  Sepiolite-HTAB Adsorption ▪ Sepiolite is an hydrous magnesium silicate characterized by its fibrous structure and internal crystal channels, and its formula Si12Mg8O30(OH)4(OH2)4 8H2O. ▪ In experimental studies, Hexadecyl Trimethyl Ammonium Bromide (HTAB), a cationic surfactant, was used in the modification process of sepiolite.  Sepiolite-HTAB Adsorption / UV/VIS Spectrometer 1,4 0,5 421 nm Peak value: 542 nm UV Region VisibleAlan UV Alan Visible Region 1,2 0,4 2,00E-05 2.10-5 M 2.10-5 M 2,00E-05 -5 M 1 1,5.10 1,50E-05 1,5.10-5 M 1,50E-05 -5 M 1.10 1,00E-05 1.10-5 M 1,00E-05 Absorbans Adsorbance Absorbans -6 M 0,3 7.10 Adsorbance 7,00E-06 0,8 7.10-6 M 7,00E-06 -6 M 5.10 5,00E-06 5.10-6 M 5,00E-06 0,6 0,2 0,4 0,1 0,2 0 0 0 200 400 600 800 1000 350 400 450 500 Dalga Boyu(nm) (nm) Dalga Boyu (nm) Wavelength (nm) Wavelength ▪ As a result of the measurements taken, it was decided that the peak point in the visible area was 542 nm and the calibration curve was drawn according to this value.  Adsorption / UV/VIS Spectrometer 0,5 0,4 Adsorbance 0,3 Absorbans 0,2 0,1 y = 20425x - 0,026 R² = 0,9907 0 0,0E+00 0 5,0E-06 5.10-6 1,0E-05 1.10-5 1,5E-05 1,5.10-5 2,0E-05 2.10-5 2,5E-05 2,5.10-5 HTAB Concentration Dalga Boyu (nm) (M) ▪ 542 nm calibration curve  Calculation of Adsorption Density Answer 1: 𝐶𝑖 − 𝐶𝑓. 𝑉 Ci: 1.10-4 mol/L 𝛤= 𝑚. 𝑆 Cf: 1.10-5 mol/L V: 20 mL = 0.02 L 1.10−4 𝑚𝑜𝑙 1.10−5 𝑚𝑜𝑙 −. (0.02 𝐿) 𝐿 𝐿 m: 100 mg = 0.1 g = 0.1 𝑔. 65 𝑚2/𝑔 S: 65 m2/g 𝜞= 𝜞= mol/m2 𝜞 = 2.8·10-7 mol/m2  Adsorption / UV/VIS Spectrometer 1,E-02 1.10-2 Region Bölge IIIIII 2) (mol/g) (mol/cm 1.10-3 1,E-03 Yoğunluğu AdsorpsiyonDensity Bölge IIII Region 1,E-04 1.10-4 Adsorption Region Bölge I I 1,E-05 1.10-5 1.10-6 1,E-06 1.10-6 1,00E-06 1.10-5 1,00E-05 1.10-4 1,00E-04 1.10-3 1,00E-03 1.10-2 1,00E-02 1.10-1 1,00E-01 Final HTAB Cd Concentration (mol/L) (mol/L)  1,E-02 1.10-2 Region Bölge IIIIII 2) (mol/g) (mol/cm 1.10-3 1,E-03 Yoğunluğu AdsorpsiyonDensity Bölge IIII Region 1,E-04 1.10-4 Sepiolite Sepiolite Sepiolite Adsorption Region Bölge I I 1,E-05 1.10-5 Monolayer 1.10-6 1,E-06 1.10-6 1,00E-06 1.10-5 1,00E-05 1.10-4 1,00E-04 1.10-3 1,00E-03 1.10-2 1,00E-02 1.10-1 1,00E-01 Final DAH Concentration (mol/L) Cd (mol/L) Parking Area In Region I, the adsorption takes place due to the ion exchange between the Mg2+ ions in the sepiolite structure and the ammonium ions of the surfactant. In Region II, the adsorption occurs due to the chain-chain interaction between the hydrocarbon chains of the amine molecules. In Region III, the plateau region indicates the beginning of the critical micelle concentration (CMC) of amine occurs. Example 2: Calculate the HTAB’s coating degree on sepiolite surfaces. Γmax: 4.2·10-6 mol/m2 1.1020 𝐶𝑜𝑎𝑡𝑖𝑛𝑔 𝐴𝑟𝑒𝑎 = A: 6.02·10 23 molecule/mol 𝛤𝑚𝑎𝑥. 𝐴 ▪ According to this calculation, the coating area is found as 39.55 Å2/molecule. ▪ Cross-sectional area of HTAB is 37.82 Å2/molecule (Sullivan vd., 1997), ▪ Surface Coating Degree is found as 0.96 (37.82/39.55). ▪ This result shows us that the HTAB covers the sepiolite surface around 96% in the plateau region. ▪ This confirms the accuracy of the adsorption isotherm obtained.  Adsorption of HTAB on Sepiolite HTAB Hydrophobic SOLUTION tail Polar head SEPIOLITE ▪ HTAB molecules with a positive surface charge used as a surfactant adsorbs onto the negatively charged sepiolite surface with the positively charged heads of HTAB and covers the surfaces by electrical attraction force. Example 3: Calculation of HTAB's Coating Degree on Sepiolite 1.1020 Γmax: 6.68·10-6 mol/m2 𝐶𝑜𝑎𝑡𝑖𝑛𝑔 𝐴𝑟𝑒𝑎 = 𝛤𝑚𝑎𝑥. 𝐴 A: 6.02·1023 molecule/mol ▪ According to this calculation, the coating area is found as 24.87 Å2/molecule. ▪ Cross-sectional area of HTAB is 37.82 Å2/molecule (Sullivan vd., 1997), ▪ Surface Coating Degree is found as 1.52 (37.82/24.87). Example 4: Calculate the HTAB’s coating degree on zeolite surfaces. Γ max: 8.10 -6 mol/m2) 1.1020 𝐶𝑜𝑎𝑡𝑖𝑛𝑔 𝐴𝑟𝑒𝑎 = A: 6.02·10 23 molecule/mol 𝛤𝑚𝑎𝑥. 𝐴 ▪ According to this calculation, the coating area is found as 20.76 Å2/molecule. ▪ Cross-sectional area of HTAB is 37.82 Å2/molecule (Sullivan vd., 1997), ▪ Surface Coating Degree is found as 1.82 (37.82/20.76).  Flotation Recovery (%) Attachment Time (ms) Flotation recovery vs. DAH Concentration Attachment time vs. DAH Concentration Zeta Potential (mV) Zeta Potential of particle vs. DAH Concentration Zeta Potential of bubble vs. DAH Concentration Receding Contact Angle (deg.) Liquid Drainage (ms) Receding contact angle vs. DAH Concentration Liquid drainage vs. DAH Concentration Adsotrption Density (mol/cm2) Adsorption density vs. DAH Concentration DAH Concentration (M) UV / VISIBLE ADSORPTION EXPERIMENT ❑ In this experiment, the adsorption of hexadecyl trimethyl ammonium bromide (HTAB) on sepiolite surface was studied. ❑ In the experiments, each HTAB solution was prepared using 1000 ppm (mg/L) HTAB stock solution (Table 1). HTAB Standard Solution Amount of HTAB Stock Water Total Concentration Solution (mL) (mL) (ppm) (mL) 1 ? ? 10 10 ? ? 10 25 ? ? 10 50 ? ? 10 100 ? ? 10 250 ? ? 10 500 ? ? 10 750 ? ? 10 1000 ? ? 10 UV / VISIBLE ADSORPTION EXPERIMENT ❑ Table 2 presents the zeta potential values of sepiolite particles as a function of HTAB concentration. HTAB Concentration Zeta Potential (ppm) (mV) 1 -32.5 10 -27.9 25 -23.4 50 -11.9 100 +8.2 250 +30.1 500 +40.8 750 +42.6 1000 +43.1 UV / VISIBLE ADSORPTION EXPERIMENT ❑ Table 3 presents the absorbance values for each HTAB solution at 542 nm. HTAB Concentration Absorbance Value (ppm) 1 0.027 5 0.082 10 0.155 25 0.395 50 0.781 100 1.536 UV / VISIBLE ADSORPTION EXPERIMENT ❑ Table 4 presents the results for sepiolite-HTAB adsorption experiments. Cf Ci Cf Adsorption Density Absorbance (ppm) (ppm) (mg/g) Value 1 0.018 10 0.149 25 0.302 50 0.409 100 0.565 250 1.255 500 4.955 750 8.754 1000 12.583 UV / VISIBLE ADSORPTION EXPERIMENT ❑ According to these results, ❑ Calculate the concentration (Cf) values of the solutions using the calibration curve, ❑ Calculate the adsorption density using Eq. 1. ❑ Draw the adsorption isotherm using the adsorption density values against Cf values and interpret the curve. HTAB Standard Solution Amount of HTAB Water Total Concentration Stock Solution (mL) (mL) (ppm) (mL) 1 0.01 9.99 10 10 0.1 9.9 10 25 0.25 9.75 10 50 0.5 9.5 10 100 1 9 10 250 2.5 7.5 10 500 5 5 10 750 7.5 2.5 10 1000 10 0 10 UV / VISIBLE ADSORPTION EXPERIMENT ❑ Zeta Potential vs. HTAB Concentration 50 40 30 Zeta Potential (mV) 20 10 0 1 10 100 1,000 -10 -20 -30 -40 -50 HTAB Concentration (ppm) UV / VISIBLE ADSORPTION EXPERIMENT ❑ Calibration Cruve 1.8 1.6 1.4 Absorbance Value 1.2 1.0 y = 0.0153x + 0.0087 0.8 R² = 0.9999 0.6 0.4 0.2 0.0 0 20 40 60 80 100 120 HTAB Concentration (ppm) UV / VISIBLE ADSORPTION EXPERIMENT ❑ Adsorption Isotherm Adsorption Density (mg/g) 1000.0 100.0 10.0 1.0 0.1 0 1 10 100 1,000 Cf (ppm)  50 40 30 Zeta Potential (mV) 20 10 0 1 10 100 1,000 -10 -20 -30 -40 -50 HTAB Concentration (ppm) 1000.0 Adsorption Density (mg/g) 100.0 10.0 1.0 0.1 0 1 10 100 1,000 Cf (ppm) Nex Week Lab 4: UV-Visible Adsorption Experiment December 20, 2024 at 9:00-11:20