Last reviewed 16 Sept 2026 · 11 min read
Nanomaterials
Nanomaterials — materials with at least one dimension in the nanoscale (about 1–100 nm); 1 nm = 10⁻⁹ m (a human hair is roughly tens of thousands of nanometres wide).
Why nanoscale properties differ
- Very high surface area to volume ratio — more atoms at the surface → higher reactivity, adsorption, catalytic activity.
- Quantum confinement effects — changes in optical, electrical and magnetic properties (e.g. colour of gold nanoparticles, band gap of quantum dots).
- Altered mechanical, thermal and melting behaviour.
FormulaSpecific surface area of spheres
= density; = particle diameter — halving the size doubles the surface area.
Classification
| Dimensions at nanoscale | Examples |
|---|---|
| 0D (all three dimensions nanoscale) | Nanoparticles, quantum dots, fullerenes (C₆₀) |
| 1D (two dimensions nanoscale) | Carbon nanotubes (CNTs), nanowires, nanorods, nanofibres |
| 2D (one dimension nanoscale) | Graphene, nanosheets, thin films, nanoclays |
| 3D nanostructured | Nanocomposites, nanoporous materials |
Important nanomaterials
| Material | Key properties | Uses |
|---|---|---|
| Carbon nanotubes (single/multi-walled) | Very high tensile strength and stiffness, electrical conductivity | Composites, sensors, self-sensing concrete (research) |
| Graphene (single layer of carbon atoms) | Extremely strong, highly conductive, impermeable | Coatings, electronics, cement composites (research) |
| Nano-silica (nano-SiO₂) | Highly pozzolanic, filler effect | Densifies concrete, accelerates hydration, reduces permeability |
| Nano-TiO₂ | Photocatalytic under UV, hydrophilic surfaces | Self-cleaning facades, glass, pavements that degrade NOx |
| Nano-clays | Layered silicates | Polymer nanocomposites, barrier properties |
| Nano-Al₂O₃, nano-Fe₂O₃, nano-CaCO₃ | Fillers, reactivity | Cement composites |
| Silver nanoparticles | Antimicrobial | Coatings, water filters |
| Zinc oxide nanoparticles | UV absorption, antimicrobial | Coatings, sunscreens |
Synthesis approaches
| Approach | Principle | Methods |
|---|---|---|
| Top-down | Breaking bulk material into nanoscale | Ball milling, lithography, laser ablation, etching |
| Bottom-up | Building from atoms/molecules | Sol–gel process, chemical vapour deposition (CVD), precipitation, hydrothermal synthesis, self-assembly |
Characterisation techniques
| Technique | Information |
|---|---|
| Scanning electron microscopy (SEM) | Surface morphology, microstructure (e.g. C–S–H, cracks) |
| Transmission electron microscopy (TEM) | Internal structure, particle size at nanoscale |
| X-ray diffraction (XRD) | Crystal structure, phases, crystallite size |
| Atomic force microscopy (AFM) | Surface topography at atomic resolution |
| BET surface area analysis | Specific surface area by gas adsorption |
| Dynamic light scattering (DLS) | Particle size distribution in suspensions |
| FTIR, Raman spectroscopy | Chemical bonds, composition |
Applications in construction
- Nano-modified concrete — nano-silica for strength and durability; CNT/graphene for crack control and self-sensing (largely research/early applications).
- Self-cleaning and air-purifying surfaces — TiO₂ coatings on facades, tiles, glass, pavement blocks.
- Protective coatings — anti-corrosion, water-repellent (superhydrophobic), anti-graffiti, UV-resistant.
- Smart windows and insulation — aerogels (nanoporous insulation), low-e coatings.
- Nanosensors for structural health monitoring.
- Water treatment — nano-filtration membranes, adsorbents.
Health, safety and environmental concerns
- Fine particles may be inhaled or penetrate cells — potential toxicity (e.g. some CNTs likened to fibre hazards).
- Handle with engineering controls, PPE, avoid dust; consider life-cycle release and disposal.
- Regulations and standards are evolving.
Environmental chemistry
Structure of the atmosphere
| Layer | Approximate altitude | Features |
|---|---|---|
| Troposphere | 0 – about 10–15 km | Weather; temperature decreases with height; most air pollution |
| Stratosphere | up to about 50 km | Ozone layer (absorbs UV); temperature increases with height |
| Mesosphere | up to about 85 km | Coldest; meteors burn |
| Thermosphere (includes ionosphere) | above | Very high temperatures; auroras; radio wave reflection |
Dry air composition by volume: N₂ ≈ 78%, O₂ ≈ 21%, Ar ≈ 0.93%, CO₂ ≈ 0.04% (and rising).
Air pollutants
| Pollutant | Main sources | Effects |
|---|---|---|
| Particulate matter (PM₁₀, PM₂.₅) | Construction dust, vehicles, industries, burning | Respiratory and cardiovascular diseases; reduced visibility |
| Carbon monoxide (CO) | Incomplete combustion (vehicles) | Combines with haemoglobin (carboxyhaemoglobin) — reduces oxygen transport |
| Sulphur dioxide (SO₂) | Coal and oil burning, smelters | Respiratory irritation, acid rain, damage to buildings and vegetation |
| Nitrogen oxides (NOx) | High-temperature combustion (vehicles, power plants) | Respiratory effects, acid rain, photochemical smog precursor |
| Hydrocarbons / VOCs | Vehicles, solvents, paints | Smog formation; some carcinogenic (benzene) |
| Ground-level ozone (O₃) | Secondary — NOx + VOCs + sunlight | Respiratory damage, crop damage |
| Lead | Earlier leaded petrol, batteries, smelting | Neurotoxic, especially in children |
| CO₂, CH₄ | Fossil fuels, cement, agriculture, landfills | Greenhouse gases |
(See Air Pollution in Environmental Engineering for standards and control devices.)
Acid rain
- Rain with pH below about 5.6 (normal rain is slightly acidic due to dissolved CO₂).
- Formed from SO₂ and NOx: SO₂ → SO₃ → H₂SO₄; NO₂ → HNO₃.
- Effects: acidification of lakes and soils, forest damage, corrosion of metals, deterioration of marble and limestone monuments (CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂ — "stone leprosy"; the Taj Mahal has been a well-known concern), damage to concrete and paints.
- Control: flue gas desulphurisation, low-sulphur fuels, catalytic converters, liming of lakes.
Photochemical smog
- Forms in sunny, warm, stagnant conditions from NOx + VOCs + sunlight → ozone, PAN (peroxyacetyl nitrate), aldehydes.
- Brownish haze; eye irritation, respiratory problems, plant damage, rubber cracking.
- Contrast: classical (London/reducing) smog — smoke + SO₂ + fog in cold humid conditions.
Ozone layer depletion
- Stratospheric ozone absorbs harmful UV-B/UV-C radiation.
- CFCs (refrigerants, aerosols, foam blowing agents) and halons release chlorine/bromine radicals under UV in the stratosphere: Cl• + O₃ → ClO• + O₂; ClO• + O → Cl• + O₂ — one chlorine atom can destroy many thousands of ozone molecules (catalytic cycle).
- Ozone hole over Antarctica (polar stratospheric clouds).
- Effects: skin cancer, cataracts, immune suppression, damage to crops and marine life.
- Montreal Protocol (1987) — phase-out of ozone-depleting substances; ozone layer is recovering slowly.
Greenhouse effect and global warming
- Greenhouse gases (CO₂, CH₄, N₂O, water vapour, fluorinated gases, O₃) are transparent to incoming short-wave solar radiation but absorb and re-emit outgoing long-wave infrared → warming.
- The natural greenhouse effect keeps earth habitable; the enhanced greenhouse effect from human emissions causes global warming and climate change — rising temperatures, sea-level rise, extreme weather, glacier retreat.
- Global warming potential (GWP) compares gases to CO₂ over a time horizon — methane and especially fluorinated gases have much higher GWP than CO₂.
- International frameworks: UNFCCC, Kyoto Protocol (1997), Paris Agreement (2015).
Water pollution chemistry
| Parameter / pollutant | Significance |
|---|---|
| Dissolved oxygen (DO) | Needed by aquatic life; saturation about 8–9 mg/L at 20–25 °C; low DO indicates organic pollution |
| Biochemical oxygen demand (BOD₅, 20 °C) | Oxygen consumed by microbes decomposing biodegradable organic matter in 5 days |
| Chemical oxygen demand (COD) | Oxygen equivalent of organic matter oxidised by strong chemical oxidant (dichromate) — includes non-biodegradable matter; COD > BOD |
| Heavy metals | Mercury (Minamata disease — methylmercury), cadmium (Itai-itai disease), lead (neurotoxicity), arsenic (arsenicosis — groundwater in parts of the Ganga–Brahmaputra plains), chromium (VI) (tanneries — carcinogenic) |
| Fluoride | Beneficial in small amounts; excess causes dental and skeletal fluorosis |
| Nitrates | Fertiliser runoff, sewage — methaemoglobinaemia ("blue baby syndrome"); eutrophication |
| Phosphates | Detergents, fertilisers — eutrophication (algal blooms, oxygen depletion) |
| Pesticides and persistent organic pollutants | Bioaccumulation and biomagnification (DDT) |
| Oil spills, microplastics, emerging contaminants | Ecological damage |
(See Water Quality and Sewage Characteristics in Environmental Engineering.)
Soil pollution
- Sources: industrial waste, excess fertilisers and pesticides, landfills and leachate, mining, e-waste, oil spills, construction and demolition waste.
- Effects: reduced fertility, contamination of crops and groundwater, health risks.
- Remediation: bioremediation, phytoremediation, soil washing, stabilisation/solidification, capping.