# Presentation: 389007

## Adsorption/Desorption of Pollutants to Nanoparticles

**Mason Tomson, V. L. Colvin**
**Xuekun Cheng, Y. Gao, R. Wahi, A. T. Kan**
**Center for Biological and Environmental Nanotechnology**
**Civil and Environmental Engineering and Chemistry Departments**
**Rice University**
**September 15, 2003**

## Adsorption/Desorption Hysteresis

- Reaction

- Uptake

- Biodegradation

- Volatilization

- Desorption

- Toxicity

**Adsorption/Desorption Hysteresis**

**Notes:**
Why do we care about adsorption to carbon nanomaterials in the environment? (Because that is one fundamental process that controls the fate and transport of pollutants in the environment. )

We all know that carbon exists in every medium in the environment, soil, water, and air. In the environment carbon has significant effects on every process of pollutant transport. Why is that? 

In the environment, pollutants could transport through all these paths. However, both organic and inorganic contaminants are known to adsorb strongly to soil carbonaceous materials. Once contaminants are adsorbed strongly to soil carbon phase, they are not available any more for any of these processes. Especially for organic contaminants, ads/des to/from organic carbon could control their fate and transport in the environment.  

If new forms of carbon, like fullerene, carbon nanotubes are introduced into the environment, will they alter the fate and transport of pollutants? We don't know yet. Because of the small size of carbon nanomaterials, they have some unique properties. So t heir behavior in the environment may not be predicted from other carbon materials. 

The purpose of this study is to understand the interaction of carbon nanomaterials with pollutants in the environment.

## Black Carbon

**Black Carbon**

**Notes:**
This pic. shows the  structure of black carbon. Black carbon is a class of organic carbon present in the environment.  It’s  mainly formed from incomplete combustion of fossil fuels or biomass. Black carbons are found in various environmental media. In the soils and sediments, 1 to 10 % of the OC could be black carbons.  

Black carbon particles can be quite porous and have a high affinity for many organic contaminants, particularly for planar aromatic compounds such as PAHs. And B.C. has been claimed to cause sorption/des. hysteresis. 

Black carbons consist of single and stacked polyaromatic sheets. C60 fullerene is composed of curved, very well organized aromatic sheets.  

Since BC could have great influence on transport and bioavailability of org. contaminants, fullerenes might have similar effects. 

## Sorption/Desorption Hysteresis

***ads***

***p***

***des***

***p***

***K***

***K***

****

**Desorption**

**Adsorption**

**Notes:**
This plot shows some observations by our group. 
Point!!!
This is ads isotherm of naph. on Lula soil; 

These are corresponding desorption isotherms for naph. desorption. 

Cleasly, ads. and des. are not reversible. 

## Slide 5

## Adsorption/Desorption Hysteresis

**Adsorption/Desorption Hysteresis**

## E. Ballesteros et al. 2000 J. Chromatography A —

Little adsorption from naphthalene aqueous solution onto fullerene C60 particles was found...

- Little adsorption from naphthalene aqueous solution onto fullerene C60 particles was found...

- Kp ~ 10

**Naphthalene Adsorption onto Original C****60**** Particles**

## Carbon Nano-Particle Transport

**Carbon Nano-Particle Transport**

## Adsorption of Organic Contaminants from Solution to C60 Fullerene

**Batch Adsorption/Desorption Study:**

**Adsorption of Organic Contaminants from Solution to C****60**** Fullerene**

**Notes:**
In my sorption/desorption study, I studied 4 different aggregation forms of C60 fullerene. 
(point!)

1) In this vial right here, is purchased C60 powder suspended in water. We call them ”C60 large aggregates" because they are actually aggregates with size up to 200 um. I added naph. soln. and rotated the sample on a mechanical rotator for a few days to conduct adsorption. 

2) In the next experiment, I first dissolved C60 in CH2Cl2, then evaporated the solvent. A C60 thin film was formed on the wall of the sample vial. Then I added naph. soln to do adsorption experiment. 

3) In the 3rd experimental protocol, I stirred the suspension of purchased C60 on a  magnetic stirrer vigorously for 2 days. The C60/water mixture became turbid and the C60 aggregates broke down to smaller size (tens of micron). Then I added naph. soln and did adsorption experiment. 

4) In the vial over here, is C60 colloidal dispersion I prepared by evaporation of benzene from the mixture of C60/benz soln. and water, similar to that proposed by Andrievsky. 

## UV/Vis Spectrum of C60 in Toluene

- Sampled from small aggregates

- 407nm

- 424nm

- 690nm

**UV/Vis Spectrum of C****60 ****in Toluene**

## Naphthalene-Carbon Adsorption Isotherms

**Naphthalene-Carbon Adsorption Isotherms**

**(1) Activated carbon**

**(2) Large aggregates**

**(3) Small aggregates**

- q=102.39C

- q=105.20C0.31

- q=104.27C0.44

**(3) Colloidal C****60**

- q=103.75C

## Adsorption/Desorption of Naphthalene(Small Aggregated and Colloidal C60 Particles)

**Adsorption**

**Adsorption**

**Desorption**

**Desorption**

**Small aggregates**

**Colloidal C****60**

**Notes:**
#1 ads: q=10 4.28 C 0.45
#2 ads: q=10 4.26 C 0.43
#3 ads: q=10 4.21 C 0.45

#1 des: q=10 3.64 C+ 10 4.0
#3 des: q=10 3.56 C + 103.9

## Adsorption/Desorption of Naphthalene to Small Aggregated C60 Particles

## Adsorption and Desorption of Organic Contaminants

**soil organic carbon**

**C****60**** Fullerene**

- 105
- 103
- 10
- 0.1

**Adsorption and Desorption of Organic Contaminants**

_**Solid Lines Represent the Rice University Dual Equilibrium Model**_

**Solution Phase Conc. (********g/ml)**

**Solid phase conc. (********g/g)**

## Carbon Nano-Particle Transport

**Carbon Nano-Particle Transport**

## What Happened During Adsorption?

**What Happened During Adsorption?**

- adsorption

- aggregation

- Small Fullerene
- Aggregates

- Naphthalene
- Adsorption

- Clusters Aggregation
- &
- Naph. Entrapment

- Naphthalene

## What Happened During Desorption?

**What Happened During Desorption?**

- “Loosely”
- Adsorbed
- Naphthalene

- desorption

- “Entrapped”
- Naphthalene

## Possible Explanations

**Possible Explanations**

- Two parts of adsorption/desorption:
-     q1: adsorption onto surfaces
-     q2: entrapment in clusters
- q1 account for  11%  adsorption;
- q2 account for  89% adsorption
- Possibility of adsorption/desorption hysteresis
- Adsorption/desorption hysteresis needs further study

## Adsorption of Cadmium to Anatase Nanoparticles

## Adsorption/Desorption of Cd to Soil

**Reversible **

**Irreversible**

## Physical Characteristics of Anatase

## TEM Images of Anatase

- Nanoparticles (RHT-69)

- Large Crystals

## Adsorption of Cadmium to Large and Nano-Anatase

**Adsorption of Cadmium to Large and Nano-Anatase**

## Langmuir Adsorption Isotherm Parameters

## Adsorption/Desorption Reversibility

**Large Crystals**

- Sigma

- RHT 69

**Nanoparticles**

## Electrochemical Properties

- Reported pzc: 5.8 - 6.1 pH

## Surface Charges and pH Adsorption Edge

- Potential Titration
- TiO2 suspension

- Cd adsorption vs. pH

## Summary

**Summary**

- States of aggregation of nanoparticles may change in various aqueous environment
- Adsorption of contaminants to the surfaces of nanoparticles is very strong
- Adsorption/desorption of organic compounds to nanoparticles might be hysteretic
- Adsorption/desorption of heavy metals onto/from nanoparticles are predictable based on surface area normalized sorption isotherm
- Nanomaterials in natural aqueous environments may affect the fate and transport of contaminants substantially

## Future

- Responsible Use
- Remediation