Lesson Plan

The Forests of Glass Tubes

1912, New York and Bologna • Cambridge / Reisner, Joule, May 2026: a solar photoreactor turns spent car-battery acid and plastic waste into clean hydrogen and acetic acid, running 260 hours without loss on a three-component carbon-nitride catalyst. • May 12, 2026

Before using this lesson plan: Read the full story or listen to the 4-minute narration (works as a bell-ringer).

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Lesson Plan: The Forests of Glass Tubes

Subject area

STEM: chemistry, photochemistry, materials science, energy and sustainability, history of science.

Recommended audience

High-school chemistry and physics (Years 11-13 / Grades 10-12)

First-year undergraduate chemistry, chemical engineering, or environmental science

General STEM enrichment for ages 14+

Lesson length

60-75 minutes (one period plus optional follow-up).

Learning objectives

By the end of the lesson, students will be able to:

Define photochemistry and explain why a light-absorbing catalyst can drive a chemical reaction that would not happen at the same temperature in the dark.

Describe Giacomo Ciamician's 1912 prediction of a solar-powered industrial chemistry and place it in the historical context of the contemporary coal economy.

Distinguish solar photovoltaics (sunlight to electricity) from direct solar photochemistry (sunlight to chemical fuel).

Describe graphitic carbon nitride (g-C3N4) as a visible-light photocatalyst, and identify Xinchen Wang's 2009 Nature Materials paper as the field's modern starting point.

Explain the chemistry of the Cambridge / Reisner 2026 reactor: how spent battery acid and discarded plastic become hydrogen and acetic acid under sunlight.

Discuss the economic, environmental, and political implications of a commercial solar-fuels industry.

Key terms

Photochemistry, photocatalyst, photon, semiconductor

Visible-light absorption, bandgap, photoexcited electron

Solar photovoltaic (PV), solar thermal, direct photochemical fuel

Graphitic carbon nitride (g-C3N4), molybdenum disulphide, cobalt co-catalyst

Polymer, ethylene glycol, sulphuric acid, acetic acid, hydrogen

Coal, anthracite, fossil fuels

Pre-class preparation

Bring or display a photograph of a typical Cambridge photoreactor (slim glass tubes containing a yellow carbon-nitride slurry under bright lights).

A periodic table.

Optional: a short clip of a working laboratory photoreactor with visible hydrogen bubbles.

Lesson outline

1. Hook (5 min): "forests of glass tubes"

Read aloud Ciamician's 1912 prediction:

"On the arid lands there will spring up industrial colonies without smoke and without smokestacks; forests of glass tubes will extend over the plains, and glass buildings will rise everywhere; inside of these will take place the photochemical processes that hitherto have been the guarded secret of the plants, but that will have been mastered by human industry, which will know how to make them bear even more abundant fruit than nature."

Pose: when was this written? (1912.) What is the prediction? (A solar-powered industrial chemistry, replacing coal.) How close are we now? (Last month, Cambridge announced one.)

2. Ciamician and the orthodoxy of 1912 (10 min)

Giacomo Ciamician (1857-1922), professor of chemistry at the University of Bologna 1889-1922. The father of modern photochemistry.

Spent 23 years systematically investigating photochemical reactions, inspired by photosynthesis in plants.

1912 lecture at the VIII International Congress of Applied Chemistry, published in Science on 27 September 1912.

The world coal industry was at its absolute peak. Coal-fired electricity, coal-fired steam, coal-fired heavy industry. Petroleum was minor and used mainly for lighting.

Ciamician's proposal was, at the time, considered visionary but impractical. The audience listened politely.

Nine Nobel Prize nominations in chemistry between 1908 and 1921. Never won.

3. What is photochemistry? (10 min)

The atom: nucleus + electrons in orbitals at quantised energy levels.

A photon of light has energy hν (Planck's relation). When a photon strikes a molecule, if the photon's energy matches a gap between two electron orbitals, an electron can be promoted from a lower to a higher orbital. This is the photoexcited state.

The photoexcited molecule has different chemistry from the ground state. It can react in ways the ground state cannot: split water, reduce carbon dioxide, isomerise, polymerise.

A photocatalyst is a molecule or solid that absorbs photons and uses the excited state to drive a useful reaction in a separate species (often water or a small organic molecule).

The most important photocatalyst in biology is chlorophyll. The most important industrial photocatalyst is now graphitic carbon nitride.

4. The diversion: photovoltaics, 1954 (5 min)

Bell Labs 1954: Chapin, Fuller and Pearson demonstrate the first practical silicon photovoltaic cell.

The 20th-century renewable-energy industry built on photovoltaics.

Photovoltaics generate electricity, not chemical fuel. To use solar electricity to make hydrogen requires a separate water-electrolysis step. This is the "two-step" pathway.

The direct photochemical route Ciamician was proposing makes the fuel in one step. The catalyst absorbs the light and produces the hydrogen on the same surface. No intervening electricity.

The two-step pathway dominated commercially through the 2010s because it could leverage cheap photovoltaics and cheap electrolysis. The one-step pathway remained academic until the catalyst materials improved.

5. Graphitic carbon nitride (10 min)

Carbon nitride (C3N4): a layered material composed of triazine or heptazine rings of carbon and nitrogen atoms in alternating positions.

Discovered theoretically in the 1980s as a hypothetical superhard material.

2009: Xinchen Wang and colleagues at Fuzhou University publish in Nature Materials that graphitic carbon nitride absorbs visible light and catalyses water splitting into hydrogen and oxygen.

The material is metal-free, made from common precursors (urea or melamine baked at 550°C), stable in water, and absorbs across the visible spectrum.

Hydrogen production rates from raw carbon nitride are too low for commercial use. The field's engineering problem since 2009: improve the catalyst, find a useful co-input, find a useful co-output.

6. The Cambridge / Reisner 2026 reactor (15 min)

Erwin Reisner: Professor of Energy and Sustainability at the Yusuf Hamied Department of Chemistry, University of Cambridge.

Spent the past decade looking for the right combination of waste-input + catalyst + valuable-output to make a commercial reactor economic.

The paper in Joule (May 2026) reports the combination.

Two waste inputs: spent sulphuric acid from lead-acid car batteries (Britain produces large volumes of this annually), and discarded plastic (also produced in enormous quantities).

The chemistry, in two steps:

Performance: ran for 260 hours of continuous operation without measurable loss. Catalyst stable. Reactor design simple and scalable.

Commercialisation: Cambridge Enterprise (Cambridge's tech-transfer arm) is spinning out the technology with UKRI Impact Acceleration Account support.

7. Why this is and is not what Ciamician imagined (5 min)

What it is: a literal forest of glass tubes, sunlight in, hydrogen out, no smokestacks. A direct demonstration that the prediction Ciamician put in print in 1912 was not just visionary but technically correct.

What it is not: a complete replacement for fossil fuels. The reactor uses waste inputs (which is excellent for waste management) but requires those waste inputs to exist. Scaling up to industrial fuel production requires significantly more capacity than today's lead-acid-battery acid and plastic-waste streams alone can supply.

The deeper insight: Ciamician was right about the catalyst, the reactor design, and the principle. The materials and the engineering took 114 years to catch up.

8. Wrap and assignment (5 min)

Pose: "Identify a current technology that you think looks like Ciamician's 1912 photochemistry: visionary, technically correct in principle, but waiting on a missing material or process. Name the missing piece."

Optional homework: write a 500-word memo from the perspective of a 2050 graduate student looking back at the 2026 Cambridge reactor, describing what the subsequent quarter-century has revealed about scaled-up solar fuels.

Discussion questions

Ciamician spent 23 years on photochemistry and never received the Nobel Prize. What does the case of Ciamician tell you about the relationship between visionary research and Nobel recognition?

The Cambridge 2026 reactor uses three catalyst components in a sandwich. What advantage does a multi-component catalyst have over a single-component one? What disadvantage?

Why is hydrogen alone not a commercially viable output for a photochemical reactor? What economic principle drove the Cambridge team to find a useful second output (acetic acid) and a useful second input (waste)?

Solar photovoltaics, invented in 1954, dominated renewable energy for 70 years. Direct solar photochemistry, predicted in 1912, has only recently begun to deliver commercial-scale reactors. What does the difference in timelines tell you about how science and engineering interact?

Ciamician closed his 1912 paper with the line about "a quieter civilisation based on the utilisation of solar energy." What did he mean by "quieter"? Compare with Bell Labs' 1954 announcement of the silicon photovoltaic.

The Cambridge reactor consumes plastic waste and battery acid. What ethical, environmental, and economic questions does this raise about waste-stream-dependent industries? (Hint: what happens if we stop producing waste?)

Extension activities

Lab demonstration (where facilities allow): illustrate photochemistry with a Friedel-Crafts photoaromatic substitution, available in undergraduate teaching kits. Discuss the role of light-absorbing dye.

Reading exercise: read Ciamician's full 1912 paper (available open-access via JSTOR) and the abstract of the May 2026 Reisner Joule paper. Identify what each predicts and what each delivers.

Calculation: estimate the area of carbon-nitride photoreactor required to produce one million tonnes of hydrogen per year, assuming the 260-hour operation rate from the Cambridge paper continues for 8 hours of daylight per day on average. Compare with the area of solar photovoltaic farms producing equivalent energy via electrolysis.

Writing assignment: write a 1000-word essay on the relationship between scientific prediction and engineering realisation. Use Ciamician's 1912 paper and the 2026 Cambridge reactor as the central case study. Address the question of why some predictions take a century to deliver.

Time Rhymes