Effect of Metal-doping of Nanoscale Maghemite on Cr(VI) Adsorption - - PowerPoint PPT Presentation

Effect of Metal-doping of Nanoscale Maghemite

• n Cr(VI) Adsorption and Nanoparticle

Dissolution

Jing Hu, Irene M. C. Lo and Guohua Chen

Environmental Engineering Program Hong Kong University of Science and Technology

Presented at the International Congress of Nanotechnology, October 31-November 3, 2005 San Francisco

Outline

 Introduction  Objectives  Methodology  Results and Discussions  Conclusions

Introduction Introduction

Hexavalent chromium, Hexavalent chromium, Cr(VI Cr(VI): ): Highly toxic but valuable Highly toxic but valuable Priority pollutants defined by USEPA Priority pollutants defined by USEPA Electroplating, acid mining, refining, Electroplating, acid mining, refining, petroleum plants petroleum plants

• High equipment costs
• Large consumption of reagents
• Large volume of sludge
• Ineffective recovery of treated metals
• Potential hazard to environment

 Chemical precipitation  Ion exchange

Technologies for heavy metal treatment

 Activated carbon adsorption

• High capital and operating cost
• Fouling
• Pretreatment
• Large intraparticle diffusion
• High regeneration cost
• Low regeneration efficiency

Magnetic nanoparticle adsorption Magnetic nanoparticle adsorption

No potential environmental No potential environmental concern concern No secondary pollution No secondary pollution Easy technical adaptation and Easy technical adaptation and maintenance maintenance Simple to desorb Simple to desorb Lower capital and operating costs Lower capital and operating costs Easy to separate from treated Easy to separate from treated water water Saved space, especially suitable Saved space, especially suitable for crowded cities for crowded cities Very short adsorption time Very short adsorption time Superior removal Superior removal Comparatively large adsorption Comparatively large adsorption capacity capacity Implications for industrial Implications for industrial applications applications Advantages Advantages

Maghemite nanoparticles for Maghemite nanoparticles for Cr(VI Cr(VI) ) removal removal

Cr(VI) adsorption equilibrium time = 10 min; 50 mg/L of Cr(VI) was reduced to be 0.05 mg/L, below discharge limit

5 10 15 20 5 10 15 20 25 30 35 40 45 50 55 60 Time (min) Am ount adsorbed (mg/g) 150 mg/L 100 mg/L 50 mg/L

How to enhance adsorption? How to enhance adsorption?

• Increase

Increase in in surface area or active sites surface area or active sites

• S

Simple imple m modification method

• dification method
• Other parameters not impaired

Other parameters not impaired significantly significantly, , e.g., adsorption rate, magnetic properties e.g., adsorption rate, magnetic properties

• Stable n

Stable nanoparticle anoparticles s

• 1. Metal-doping technique
• 2. Inorganic coating technique

Objectives Objectives

• Promotion of adsorption by metal

Promotion of adsorption by metal-

• doping

doping

• Inhibition of dissolution by metal

Inhibition of dissolution by metal-

• doping

doping

• Mechanism studies by Raman spectroscopy

Mechanism studies by Raman spectroscopy

Materials and Methods Materials and Methods

  Adsorbent Adsorbent

Metal Metal-doped doped γ-

• Fe

Fe2O O3 nanoparticle (Me= Al, Mg, Cu, Zn, Ni) nanoparticle (Me= Al, Mg, Cu, Zn, Ni)

  Adsorbate

Adsorbate

100 mg/L K 100 mg/L K2CrO CrO4

4 + 0.1 M NaNO

+ 0.1 M NaNO3

3

  Batch test

Batch test

Experimental conditions: contact time: 60 min; pH: 2.5; Experimental conditions: contact time: 60 min; pH: 2.5; shaking rate: 200 rpm; room temp shaking rate: 200 rpm; room temperature: 25 erature: 25o

• C

C

  Mechanism study Mechanism study

Sample for Raman: 5, 50, 100 mg/L Sample for Raman: 5, 50, 100 mg/L Cr(VI Cr(VI) at pH 2.5, 6.5, 8.5 ) at pH 2.5, 6.5, 8.5

XRF Elemental analysis Raman spectroscopy Complexation BET Analyzer Surface area VSM Magnetism XRD Particle structure TEM Particle dimension ZETA PLUS Zeta potential pH Meter pH ICP Cr Analytical methods Parameters

Analytical Methods Analytical Methods

Raman spectroscopic studies Raman spectroscopic studies

  Establish symmetry of surface species Establish symmetry of surface species   Distinguish inner Distinguish inner-

• sphere from outer

sphere from outer-

• sphere

sphere

(David et al., 1978; (David et al., 1978; Tejedor Tejedor and Anderson, 1990) and Anderson, 1990)

  Raman spectroscopic data about PO Raman spectroscopic data about PO4

43 3-

• , CO

, CO3

32 2-

• , SeO

, SeO4

42 2-

• ,

, SO SO4

4 2 2-, and AsO

, and AsO4

4 2- adsorption onto Fe/Al oxides available

adsorption onto Fe/Al oxides available

( (Schulthess Schulthess and McCarthy, 1990; Su and Suarez, 1998; and McCarthy, 1990; Su and Suarez, 1998; Wijnja Wijnja and Cristian, 2000; Goldberg and Johnston, 2001) and Cristian, 2000; Goldberg and Johnston, 2001)

  Little detailed information on Raman spectroscopic Little detailed information on Raman spectroscopic study of CrO study of CrO4

2- adsorption onto (modified) iron oxide

adsorption onto (modified) iron oxide

Modification of synthesizing methods Modification of synthesizing methods

Surfactant Fe2+, Fe3+, NH4OH ( or +Me) Magnetite particle

pH 8.0 (or 10)

Maghemite nanogel Oil bath Maghemite nanoparticles (< 20 nm, ~ 250 m2/g) Ethanol washing Octyl ether

• Sol-gel method

Fe2+, Fe3+, NH4OH Magnetite particle

pH 8.0

Maghemite aggregate

250oC oven

Maghemite nanoparticles (> 30 nm, < 80 m2/g)

Grinding

• Precipitation method

Calcination

Nanoparticle Synthesis Method (sol Nanoparticle Synthesis Method (sol-

• gel)

gel)

N2 gas 1.5 M NH4OH

Al-doped magnetite (Fe3O4)

condenser 250oC oil bath

air

Thermocouple

Al-doped maghemite (γ-Fe2O3)

TEM images of Al TEM images of Al-

• doped

doped γ-Fe2O3

Undoped γ-Fe2O3 Al-doped γ-Fe2O3 with 7.5% of Al Al-doped γ-Fe2O3 with 13.1% of Al Doping of Al results in preferential crystal growth along [100] direction producing irregular shaped, platy particles, at expense of crystal thickness (Schulze, 1984)

XRD patterns of undoped & Al XRD patterns of undoped & Al-

• doped

doped γ-Fe2O3

100 200 300 400 500 600 10 15 20 25 30 35 40 45 50 55 60 65 70 Degrees 2-Theta Counts Al-doping γ-Fe2O3 γ-Fe2O3

A definite proof of structural incorporation can be produced from a shift in position of XRD peaks, but doping would not change original structure

Hysteresis loops of Al Hysteresis loops of Al-

• doped

doped γ-Fe2O3

Magnetic properties decreased with increasing Al dosage

• 4
• 3
• 2
• 1

1 2 3 4

• 10000
• 8000
• 6000
• 4000
• 2000

2000 4000 6000 8000 10000 Field (Oe) Moment (emu) γ-Fe2O3 7.5% Al-dopant γ-Fe2O3 9.3% Al-dopant γ-Fe2O3 11%Al-dopant γ-Fe2O3 13.1%Al-dopant γ-Fe2O3

Effect of doped metal on Effect of doped metal on Cr(VI Cr(VI) adsorption ) adsorption

70 72 74 76 78 80 82 84 86 88 No- Al- Ni- Cu- Zn- Mg- Metal-dopant maghemite Removal efficiency (%)

Al-, Cu- and Mg- doping enhanced adsorption capacity; while Cu- and Ni-doping decreased adsorption capacity of previous γ-Fe2O3

Adsorption and separation Adsorption and separation

/ / 1.14 1.14 1.25 1.25 2.26 2.26 3.48 3.48 ( (emu emu) ) Magnetic Magnetic properties properties 210 210 198 198 191 191 182 182 162 162 (m (m2

2/g)

/g) Surface Surface area area 10 10 90 90 88.9 88.9 13.1 13.1 5 5 60 60 87.5 87.5 11.0 11.0 1 1 30 30 86.7 86.7 9.3 9.3 0.5 0.5 25 25 84.3 84.3 7.5 7.5 0.1 0.1 10 10 79.8 79.8 (min) (min) (min) (min) (%) (%) (%) (%) Separation Separation Time Time Equilibrium Equilibrium time time Adsorption Adsorption efficiency efficiency Al/(Al+Fe) Al/(Al+Fe)

9.3 191 86.7 30 1.78 1

Adsorption mechanism (Raman) Adsorption mechanism (Raman)

— — Cr(VI Cr(VI) adsorption onto Al ) adsorption onto Al-

• doped

doped γ-Fe2O3

200 300 400 500 600 700 800 900 1000 1100 1200 Raman shift (cm-1) Counts

K2CrO4 Al-doped γ-Fe2O3 γ-Fe2O3

342 848 882 365 498 679 720

Vibrations for the free CrO4

2- are all Raman active: the nondegenerate v1 at 848

cm-1, the doubly degenerate v2 at 342 cm-1, the triply degenerate v3 at 882 cm-1, and the triply degenerate v4 at 365 cm-1

200 300 400 500 600 700 800 900 1000 1100 1200 Raman shift (cm-1) Counts

831

369 848 840 1046 670 719 502 365 pH 2.5 pH 6.5 pH 8.5 858 876 926 863 932 670 719 480 480 480 502 502 339 354 338

359

341 670 719

Raman spectra Raman spectra

— — Effect of pH Effect of pH

V2 V4 V1 V3

γ-Fe2O3 NO3

100 mg/L Cr(VI) + 5 g/L Al-doped γ-Fe2O3 at pH 2.5, 6.5, 8.5

Raman spectra Raman spectra

— — Effect of surface loading Effect of surface loading

200 300 400 500 600 700 800 900 1000 1100 1200 Raman shift (cm-1) Counts 831 369 835 837 670 719 502 100 mg/L Cr(VI) 50 mg/L Cr(VI) 5 mg/L Cr(VI) 858 876 926 867 912 670 670 719 719 480 480 482 500 502 331 354 338 359 331 366 372 868 894 918

V2 V1 V3 V4 5, 50, 100 mg/L Cr(VI) + 5 g/L Al-doped γ-Fe2O3 at pH 2.5

Vibrations between CrO Vibrations between CrO42

2-

• and Al

and Al-

• doped

doped γ γ-

• Fe

Fe2

2O

O3

3 354 354 / / 339 339 848 848 8.5 8.5 100 100 Al Al-

• doped

doped γ γ-

• Fe

Fe2O O3

3

365 365 932 932 863 863 341 341 840 840 6.5 6.5 100 100 Al Al-

• doped

doped γ γ-

• Fe

Fe2

2O

O3

3

369 369 359 359 926 926 876 876 858 858 338 338 831 831 2.5 2.5 100 100 Al Al-

• doped

doped γ γ-

• Fe

Fe2

2O

O3

3

366 366 894 894 868 868 331 331 835 835 2.5 2.5 50 50 Al Al-

• doped

doped γ γ-

• Fe

Fe2

2O

O3

3

360 360 912 912 867 867 331 331 837 837 2.5 2.5 5 5 Al Al-

• doped

doped γ γ-

• Fe

Fe2O3

3

365 365 882 882 342 342 848 848 K K2CrO CrO4 ( (aq aq) ) ν ν4 ν ν3 ν2

2

ν ν1 Frequency (cm Frequency (cm-

• 1

1)

) pH pH Cr(VI Cr(VI) ) (mg/L) (mg/L) Species Species

Inner Inner-

• sphere complex between

sphere complex between Cr(VI Cr(VI) and ) and Al Al-

• doped

doped γ-Fe2O3

Monodentate Bidentate mononuclear* Bidentate binuclear*

M M O Cr O O O O O M M M O O O Cr O O O M M M O O Cr O O O O O

(* Together with data from Hiemstra et al., 1989; McBride, 1994; Fendorf et al., 1997; Wijnja and Schuthess, 2000)

O O O O

Increasing pH Increasing surface loading

Adsorption isotherms Adsorption isotherms

0.997 0.997 0.319 0.319 19.42 19.42 Pure Pure γ γ-

• Fe

Fe2O O3 0.993 0.993 0.138 0.138 22.68 22.68 Al Al-

• doped

doped γ-

• Fe

Fe2

2O

O3 b (L/mg) b (L/mg) q qm (mg/g) (mg/g) R R2

2

Langmuir constants Langmuir constants Adsorbent Adsorbent

0.0 1.0 2.0 3.0 4.0 5.0 6.0 20 40 60 80 100 120 Ce (mg/L) Ce/qe (g nanoparticle/L solution) γ-Fe2O3 Al-doped γ-Fe2O3

Comparison of adsorbents Comparison of adsorbents

(Aoyama and (Aoyama and Tsuda Tsuda, 2001) , 2001) 3.0 3.0 48 48 31.25 31.25 Larch bark Larch bark Present study Present study 2.5 2.5 0.5 0.5 22.68 22.68 Al Al-doped doped γ-Fe Fe2O O3

3

(Low et al., 2001) (Low et al., 2001) 2.0 2.0 8 8 18.94 18.94 Spent grain Spent grain (Cimino Cimino et al.,2000) et al.,2000) 2.0 2.0 5 5 17.7 17.7 Hazelnut shell Hazelnut shell (Acar Acar and and Malkoc Malkoc, 2004) , 2004) 1.0 1.0 1.33 1.33 16.13 16.13 Beech sawdust Beech sawdust ( (Sandhya Sandhya and and Tonni Tonni, 2004) , 2004) 4.0 4.0 3 3 15.47 15.47 Acti Activated vated carbon carbon ( (Weng Weng et al, 1997) et al, 1997) 2.5 2.5 24 24 14.56 14.56 Anatase Anatase ( (Gupta Gupta et al., 1999) et al., 1999) 4.0 4.0 8 8 11.7 11.7 Aluminum Aluminum oxide

• xide

(Dantas et al., 2001) (Dantas et al., 2001) 3.0 3.0 2 2 11.55 11.55 Diatomite Diatomite ( (Srivastava Srivastava et al., 1997) et al., 1997) 1.0 1.0 6 6 7.5 7.5 Blast Blast-

• furnace slag

furnace slag (Selvaraj et al., 2003) (Selvaraj et al., 2003) 3.0 3.0 1.75 1.75 5.7 5.7 Distillery sludge Distillery sludge ( (Lalvani Lalvani et al, 2000) et al, 2000) 2.5 2.5 24 24 5.64 5.64 Lignin Lignin ( (Selvi Selvi et al., 2001) et al., 2001) 3.0 3.0 3 3 3.46 3.46 Coconut tree sawdust Coconut tree sawdust References References Optimum pH Optimum pH Equilibrium time (h) Equilibrium time (h) q qm (mg/g) (mg/g) Type of adsorbents Type of adsorbents Note: Cr(VI) Adsorption capacity and equilibrium time at room temperature of 22.5 2.5oC

Prevention of nanoparticle dissolution Prevention of nanoparticle dissolution

1) Al 1) Al-

• O bond energy (513 kJ mol

O bond energy (513 kJ mol-

• 1

1) > Fe

) > Fe-

• O bond energy (390 kJ mol

O bond energy (390 kJ mol-

• 1

1),

), 2) More energy to remove simultaneously two center atoms due to 2) More energy to remove simultaneously two center atoms due to effect of binuclear complexes effect of binuclear complexes (Cornell et al., 2003)

(Cornell et al., 2003)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 pH Fraction of metal dissolved (100%) 10 20 30 40 50 60 70 80 90 100 Cr(VI) removal efficiency (%)

Fe from maghemite Fe from Al-doped maghemite Al from Al-doped maghemite

Conclusions Conclusions

• Optimal Al dosage is

Optimal Al dosage is 9.3 9.3 mol% mol%

• Enhanced adsorption capacity from

Enhanced adsorption capacity from 19.4 19.4 mg/g mg/g to to 22.7 22.7 mg/g by Al mg/g by Al-

• doping

doping

• Insignificant

Insignificant nanoparticle dissolution under nanoparticle dissolution under experimental condition; Al experimental condition; Al-

• doping inhibited

doping inhibited dissolution by dissolution by 30% 30%

• Complexation changed from outer

Complexation changed from outer-

• sphere into

sphere into inner inner-

• sphere complexation

sphere complexation by Al by Al-

• doping

doping